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 $129.87   3.182%   $134.0025   $134.00   $134.00   $134.00  
  Purchase #2 $35.39   5.510%   $37.34   $37.34   $37.35   $37.30  
  Purchase #3 $197.35   8.617%   $214.3556   $214.36   $214.35   $214.40  
  Purchase #4 $210.94   6.347%   $224.3284   $224.33   $224.35   $224.30  
  Purchase #5 $209.59   12.397%   $235.5729   $235.57   $235.55   $235.60  
  Purchase #6 $9.46   4.471%   $9.883   $9.88   $9.90   $9.90  
  Purchase #7 $205.56   9.407%   $224.897   $224.90   $224.90   $224.90  
  7 purchase totals = $998.16       $1,080.3794   $1,080.38   $1,080.40   $1,080.40