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 $114.88   12.263%   $128.9677   $128.97   $128.95   $129.00  
  Purchase #2 $184.55   10.357%   $203.6638   $203.66   $203.65   $203.70  
  Purchase #3 $152.77   13.353%   $173.1694   $173.17   $173.15   $173.20  
  Purchase #4 $248.53   3.437%   $257.072   $257.07   $257.05   $257.10  
  Purchase #5 $59.49   9.805%   $65.323   $65.32   $65.30   $65.30  
  Purchase #6 $195.30   4.360%   $203.8151   $203.82   $203.80   $203.80  
  Purchase #7 $138.36   5.649%   $146.176   $146.18   $146.20   $146.20  
  7 purchase totals = $1,093.88       $1,178.1870   $1,178.19   $1,178.10   $1,178.30