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 $194.69   4.760%   $203.9572   $203.96   $203.95   $204.00  
  Purchase #2 $138.33   6.180%   $146.8788   $146.88   $146.90   $146.90  
  Purchase #3 $114.80   9.516%   $125.7244   $125.72   $125.70   $125.70  
  Purchase #4 $229.69   8.319%   $248.7979   $248.80   $248.80   $248.80  
  Purchase #5 $31.96   12.358%   $35.9096   $35.91   $35.90   $35.90  
  Purchase #6 $146.47   4.539%   $153.1183   $153.12   $153.10   $153.10  
  Purchase #7 $35.69   6.226%   $37.9121   $37.91   $37.90   $37.90  
  7 purchase totals = $891.63       $952.2983   $952.30   $952.25   $952.30