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 $118.25   7.510%   $127.1306   $127.13   $127.15   $127.10  
  Purchase #2 $66.80   7.554%   $71.8461   $71.85   $71.85   $71.80  
  Purchase #3 $246.42   11.262%   $274.1718   $274.17   $274.15   $274.20  
  Purchase #4 $21.84   12.492%   $24.5683   $24.57   $24.55   $24.60  
  Purchase #5 $101.90   6.114%   $108.1302   $108.13   $108.15   $108.10  
  Purchase #6 $67.46   3.465%   $69.7975   $69.80   $69.80   $69.80  
  Purchase #7 $133.93   11.218%   $148.9543   $148.95   $148.95   $149.00  
  7 purchase totals = $756.60       $824.5988   $824.60   $824.60   $824.60