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 $24.61   6.182%   $26.1314   $26.13   $26.15   $26.10  
  Purchase #2 $172.62   4.387%   $180.1928   $180.19   $180.20   $180.20  
  Purchase #3 $248.68   3.327%   $256.9536   $256.95   $256.95   $257.00  
  Purchase #4 $122.78   9.584%   $134.5472   $134.55   $134.55   $134.50  
  Purchase #5 $161.38   12.743%   $181.9447   $181.94   $181.95   $181.90  
  Purchase #6 $218.35   11.822%   $244.1633   $244.16   $244.15   $244.20  
  Purchase #7 $165.42   11.443%   $184.349   $184.35   $184.35   $184.30  
  7 purchase totals = $1,113.84       $1,208.2820   $1,208.27   $1,208.30   $1,208.20