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 $31.42   13.311%   $35.6023   $35.60   $35.60   $35.60  
  Purchase #2 $167.55   9.671%   $183.7538   $183.75   $183.75   $183.80  
  Purchase #3 $31.44   3.712%   $32.6071   $32.61   $32.60   $32.60  
  Purchase #4 $45.80   12.536%   $51.5415   $51.54   $51.55   $51.50  
  Purchase #5 $104.85   5.836%   $110.969   $110.97   $110.95   $111.00  
  Purchase #6 $204.49   5.533%   $215.8044   $215.80   $215.80   $215.80  
  Purchase #7 $97.31   5.231%   $102.4003   $102.40   $102.40   $102.40  
  7 purchase totals = $682.86       $732.6784   $732.67   $732.65   $732.70