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 $27.91   6.233%   $29.6496   $29.65   $29.65   $29.60  
  Purchase #2 $192.71   6.188%   $204.6349   $204.63   $204.65   $204.60  
  Purchase #3 $48.31   13.635%   $54.8971   $54.90   $54.90   $54.90  
  Purchase #4 $80.82   12.788%   $91.1553   $91.16   $91.15   $91.20  
  Purchase #5 $226.25   5.872%   $239.5354   $239.54   $239.55   $239.50  
  Purchase #6 $96.94   5.728%   $102.4927   $102.49   $102.50   $102.50  
  Purchase #7 $29.91   3.427%   $30.935   $30.94   $30.95   $30.90  
  7 purchase totals = $702.85       $753.3000   $753.31   $753.35   $753.20