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 $247.54   7.370%   $265.7837   $265.78   $265.80   $265.80  
  Purchase #2 $104.63   11.355%   $116.5107   $116.51   $116.50   $116.50  
  Purchase #3 $114.43   10.661%   $126.6294   $126.63   $126.65   $126.60  
  Purchase #4 $45.37   6.276%   $48.2174   $48.22   $48.20   $48.20  
  Purchase #5 $37.27   11.204%   $41.4457   $41.45   $41.45   $41.40  
  Purchase #6 $156.30   4.846%   $163.8743   $163.87   $163.85   $163.90  
  Purchase #7 $245.54   6.106%   $260.5327   $260.53   $260.55   $260.50  
  7 purchase totals = $951.08       $1,022.9939   $1,022.99   $1,023.00   $1,022.90