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 $135.56   11.204%   $150.7481   $150.75   $150.75   $150.70  
  Purchase #2 $65.77   11.206%   $73.1402   $73.14   $73.15   $73.10  
  Purchase #3 $61.69   4.846%   $64.6795   $64.68   $64.70   $64.70  
  Purchase #4 $203.41   10.303%   $224.3673   $224.37   $224.35   $224.40  
  Purchase #5 $153.68   6.452%   $163.5954   $163.60   $163.60   $163.60  
  Purchase #6 $211.75   5.773%   $223.9743   $223.97   $223.95   $224.00  
  Purchase #7 $43.49   6.369%   $46.2599   $46.26   $46.25   $46.30  
  7 purchase totals = $875.35       $946.7647   $946.77   $946.75   $946.80