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 $56.93   13.692%   $64.7249   $64.72   $64.70   $64.70  
  Purchase #2 $215.57   5.141%   $226.6525   $226.65   $226.65   $226.70  
  Purchase #3 $243.48   3.193%   $251.2543   $251.25   $251.25   $251.30  
  Purchase #4 $44.34   6.760%   $47.3374   $47.34   $47.35   $47.30  
  Purchase #5 $11.63   7.776%   $12.5343   $12.53   $12.55   $12.50  
  Purchase #6 $139.51   4.432%   $145.6931   $145.69   $145.70   $145.70  
  Purchase #7 $245.29   13.234%   $277.7517   $277.75   $277.75   $277.80  
  7 purchase totals = $956.75       $1,025.9482   $1,025.93   $1,025.95   $1,026.00