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 $55.96   10.626%   $61.9063   $61.91   $61.90   $61.90  
  Purchase #2 $41.27   4.203%   $43.0046   $43.00   $43.00   $43.00  
  Purchase #3 $243.70   12.654%   $274.5378   $274.54   $274.55   $274.50  
  Purchase #4 $154.92   9.274%   $169.2873   $169.29   $169.30   $169.30  
  Purchase #5 $188.95   10.386%   $208.5743   $208.57   $208.55   $208.60  
  Purchase #6 $244.75   10.581%   $270.647   $270.65   $270.65   $270.60  
  Purchase #7 $89.61   13.658%   $101.8489   $101.85   $101.85   $101.80  
  7 purchase totals = $1,019.16       $1,129.8062   $1,129.81   $1,129.80   $1,129.70