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 $216.75   11.549%   $241.7825   $241.78   $241.80   $241.80  
  Purchase #2 $170.45   7.874%   $183.8712   $183.87   $183.85   $183.90  
  Purchase #3 $92.75   4.813%   $97.2141   $97.21   $97.20   $97.20  
  Purchase #4 $222.34   12.847%   $250.904   $250.90   $250.90   $250.90  
  Purchase #5 $161.29   10.441%   $178.1303   $178.13   $178.15   $178.10  
  Purchase #6 $184.28   10.666%   $203.9353   $203.94   $203.95   $203.90  
  Purchase #7 $13.40   11.321%   $14.917   $14.92   $14.90   $14.90  
  7 purchase totals = $1,061.26       $1,170.7544   $1,170.75   $1,170.75   $1,170.70