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 $75.98   12.773%   $85.6849   $85.68   $85.70   $85.70  
  Purchase #2 $97.83   11.638%   $109.2155   $109.22   $109.20   $109.20  
  Purchase #3 $54.37   12.376%   $61.0988   $61.10   $61.10   $61.10  
  Purchase #4 $26.40   5.137%   $27.7562   $27.76   $27.75   $27.80  
  Purchase #5 $31.60   11.578%   $35.2586   $35.26   $35.25   $35.30  
  Purchase #6 $164.50   9.363%   $179.9021   $179.90   $179.90   $179.90  
  Purchase #7 $230.43   9.840%   $253.1043   $253.10   $253.10   $253.10  
  7 purchase totals = $681.11       $752.0204   $752.02   $752.00   $752.10