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 $64.30   4.571%   $67.2392   $67.24   $67.25   $67.20  
  Purchase #2 $60.45   13.586%   $68.6627   $68.66   $68.65   $68.70  
  Purchase #3 $62.43   13.438%   $70.8193   $70.82   $70.80   $70.80  
  Purchase #4 $115.42   11.302%   $128.4648   $128.46   $128.45   $128.50  
  Purchase #5 $200.48   10.223%   $220.9751   $220.98   $221.00   $221.00  
  Purchase #6 $235.56   12.238%   $264.3878   $264.39   $264.40   $264.40  
  Purchase #7 $170.39   13.492%   $193.379   $193.38   $193.40   $193.40  
  7 purchase totals = $909.03       $1,013.9279   $1,013.93   $1,013.95   $1,014.00