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 $52.33   7.486%   $56.2474   $56.25   $56.25   $56.20  
  Purchase #2 $75.90   6.556%   $80.876   $80.88   $80.90   $80.90  
  Purchase #3 $38.44   8.381%   $41.6617   $41.66   $41.65   $41.70  
  Purchase #4 $28.74   12.287%   $32.2713   $32.27   $32.25   $32.30  
  Purchase #5 $226.90   11.742%   $253.5426   $253.54   $253.55   $253.50  
  Purchase #6 $238.40   7.450%   $256.1608   $256.16   $256.15   $256.20  
  Purchase #7 $90.28   7.351%   $96.9165   $96.92   $96.90   $96.90  
  7 purchase totals = $750.99       $817.6763   $817.68   $817.65   $817.70