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 $46.95   5.255%   $49.4172   $49.42   $49.40   $49.40  
  Purchase #2 $30.93   6.189%   $32.8443   $32.84   $32.85   $32.80  
  Purchase #3 $227.70   12.489%   $256.1375   $256.14   $256.15   $256.10  
  Purchase #4 $49.89   8.197%   $53.9795   $53.98   $54.00   $54.00  
  Purchase #5 $88.40   5.232%   $93.0251   $93.03   $93.05   $93.00  
  Purchase #6 $238.68   11.159%   $265.3143   $265.31   $265.30   $265.30  
  Purchase #7 $36.92   11.836%   $41.2899   $41.29   $41.30   $41.30  
  7 purchase totals = $719.47       $792.0078   $792.01   $792.05   $791.90