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 $89.70   4.545%   $93.7769   $93.78   $93.80   $93.80  
  Purchase #2 $206.76   8.266%   $223.8508   $223.85   $223.85   $223.90  
  Purchase #3 $22.72   11.330%   $25.2942   $25.29   $25.30   $25.30  
  Purchase #4 $245.88   4.262%   $256.3594   $256.36   $256.35   $256.40  
  Purchase #5 $205.62   5.375%   $216.6721   $216.67   $216.65   $216.70  
  Purchase #6 $117.96   11.146%   $131.1078   $131.11   $131.10   $131.10  
  Purchase #7 $50.68   6.659%   $54.0548   $54.05   $54.05   $54.10  
  7 purchase totals = $939.32       $1,001.1160   $1,001.11   $1,001.10   $1,001.30