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 $113.72   10.742%   $125.9358   $125.94   $125.95   $125.90  
  Purchase #2 $191.59   8.862%   $208.5687   $208.57   $208.55   $208.60  
  Purchase #3 $216.28   10.231%   $238.4076   $238.41   $238.40   $238.40  
  Purchase #4 $15.74   5.865%   $16.6632   $16.66   $16.65   $16.70  
  Purchase #5 $180.72   7.709%   $194.6517   $194.65   $194.65   $194.70  
  Purchase #6 $156.42   9.492%   $171.2674   $171.27   $171.25   $171.30  
  Purchase #7 $59.96   4.488%   $62.651   $62.65   $62.65   $62.70  
  7 purchase totals = $934.43       $1,018.1454   $1,018.15   $1,018.10   $1,018.30