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 $58.25   10.775%   $64.5264   $64.53   $64.55   $64.50  
  Purchase #2 $111.45   5.523%   $117.6054   $117.61   $117.60   $117.60  
  Purchase #3 $84.53   4.674%   $88.4809   $88.48   $88.50   $88.50  
  Purchase #4 $95.61   12.327%   $107.3958   $107.40   $107.40   $107.40  
  Purchase #5 $115.93   8.629%   $125.9336   $125.93   $125.95   $125.90  
  Purchase #6 $179.30   13.787%   $204.0201   $204.02   $204.00   $204.00  
  Purchase #7 $143.37   3.191%   $147.9449   $147.94   $147.95   $147.90  
  7 purchase totals = $788.44       $855.9071   $855.91   $855.95   $855.80