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 $51.63   13.816%   $58.7632   $58.76   $58.75   $58.80  
  Purchase #2 $160.94   5.806%   $170.2842   $170.28   $170.30   $170.30  
  Purchase #3 $138.41   5.715%   $146.3201   $146.32   $146.30   $146.30  
  Purchase #4 $54.30   11.554%   $60.5738   $60.57   $60.55   $60.60  
  Purchase #5 $58.55   6.867%   $62.5706   $62.57   $62.55   $62.60  
  Purchase #6 $214.70   6.840%   $229.3855   $229.39   $229.40   $229.40  
  Purchase #7 $75.70   11.396%   $84.3268   $84.33   $84.35   $84.30  
  7 purchase totals = $754.23       $812.2242   $812.22   $812.20   $812.30