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 $209.33   6.542%   $223.0244   $223.02   $223.00   $223.00  
  Purchase #2 $225.61   11.166%   $250.8016   $250.80   $250.80   $250.80  
  Purchase #3 $39.73   5.114%   $41.7618   $41.76   $41.75   $41.80  
  Purchase #4 $173.43   13.796%   $197.3564   $197.36   $197.35   $197.40  
  Purchase #5 $82.30   5.774%   $87.052   $87.05   $87.05   $87.10  
  Purchase #6 $13.33   12.266%   $14.9651   $14.97   $14.95   $15.00  
  Purchase #7 $224.27   8.210%   $242.6826   $242.68   $242.70   $242.70  
  7 purchase totals = $968.00       $1,057.6439   $1,057.64   $1,057.60   $1,057.80