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 $53.46   12.192%   $59.9778   $59.98   $60.00   $60.00  
  Purchase #2 $66.92   11.479%   $74.6017   $74.60   $74.60   $74.60  
  Purchase #3 $104.71   7.600%   $112.668   $112.67   $112.65   $112.70  
  Purchase #4 $99.49   5.494%   $104.956   $104.96   $104.95   $105.00  
  Purchase #5 $130.88   5.171%   $137.6478   $137.65   $137.65   $137.60  
  Purchase #6 $130.49   7.617%   $140.4294   $140.43   $140.45   $140.40  
  Purchase #7 $27.33   6.651%   $29.1477   $29.15   $29.15   $29.10  
  7 purchase totals = $613.28       $659.4284   $659.44   $659.45   $659.40