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 $54.65   13.679%   $62.1256   $62.13   $62.15   $62.10  
  Purchase #2 $220.29   5.468%   $232.3355   $232.34   $232.35   $232.30  
  Purchase #3 $151.81   6.290%   $161.3588   $161.36   $161.35   $161.40  
  Purchase #4 $87.51   7.252%   $93.8562   $93.86   $93.85   $93.90  
  Purchase #5 $79.40   4.114%   $82.6665   $82.67   $82.65   $82.70  
  Purchase #6 $232.68   8.763%   $253.0697   $253.07   $253.05   $253.10  
  Purchase #7 $118.68   3.686%   $123.0545   $123.05   $123.05   $123.10  
  7 purchase totals = $945.02       $1,008.4668   $1,008.48   $1,008.45   $1,008.60