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 $55.41   9.104%   $60.4545   $60.45   $60.45   $60.50  
  Purchase #2 $234.39   11.249%   $260.7565   $260.76   $260.75   $260.80  
  Purchase #3 $68.76   7.752%   $74.0903   $74.09   $74.10   $74.10  
  Purchase #4 $167.42   6.311%   $177.9859   $177.99   $178.00   $178.00  
  Purchase #5 $150.85   13.136%   $170.6657   $170.67   $170.65   $170.70  
  Purchase #6 $207.96   10.434%   $229.6585   $229.66   $229.65   $229.70  
  Purchase #7 $47.26   12.161%   $53.0073   $53.01   $53.00   $53.00  
  7 purchase totals = $932.05       $1,026.6187   $1,026.63   $1,026.60   $1,026.80