Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $181.66   11.239%   $202.0768   $202.08   $202.10   $202.10  
  Purchase #2 $205.56   13.321%   $232.9426   $232.94   $232.95   $232.90  
  Purchase #3 $232.53   10.616%   $257.2154   $257.22   $257.20   $257.20  
  Purchase #4 $221.61   8.199%   $239.7798   $239.78   $239.80   $239.80  
  Purchase #5 $183.70   3.540%   $190.203   $190.20   $190.20   $190.20  
  Purchase #6 $151.52   3.312%   $156.5383   $156.54   $156.55   $156.50  
  Purchase #7 $188.70   11.534%   $210.4647   $210.46   $210.45   $210.50  
  7 purchase totals = $1,365.28       $1,489.2206   $1,489.22   $1,489.25   $1,489.20