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 $179.99   13.693%   $204.636   $204.64   $204.65   $204.60  
  Purchase #2 $236.50   11.197%   $262.9809   $262.98   $263.00   $263.00  
  Purchase #3 $186.95   12.322%   $209.986   $209.99   $210.00   $210.00  
  Purchase #4 $250.86   7.262%   $269.0775   $269.08   $269.10   $269.10  
  Purchase #5 $168.47   3.591%   $174.5198   $174.52   $174.50   $174.50  
  Purchase #6 $124.80   12.341%   $140.2016   $140.20   $140.20   $140.20  
  Purchase #7 $71.61   4.180%   $74.6033   $74.60   $74.60   $74.60  
  7 purchase totals = $1,219.18       $1,336.0051   $1,336.01   $1,336.05   $1,336.00