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 $67.25   13.424%   $76.2776   $76.28   $76.30   $76.30  
  Purchase #2 $44.94   10.396%   $49.612   $49.61   $49.60   $49.60  
  Purchase #3 $206.58   10.649%   $228.5787   $228.58   $228.60   $228.60  
  Purchase #4 $68.32   10.498%   $75.4922   $75.49   $75.50   $75.50  
  Purchase #5 $204.27   12.211%   $229.2134   $229.21   $229.20   $229.20  
  Purchase #6 $8.29   13.405%   $9.4013   $9.40   $9.40   $9.40  
  Purchase #7 $217.63   8.167%   $235.4038   $235.40   $235.40   $235.40  
  7 purchase totals = $817.28       $903.9790   $903.97   $904.00   $904.00