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 $120.27   4.752%   $125.9852   $125.99   $126.00   $126.00  
  Purchase #2 $232.58   12.308%   $261.2059   $261.21   $261.20   $261.20  
  Purchase #3 $125.33   8.431%   $135.8966   $135.90   $135.90   $135.90  
  Purchase #4 $177.93   8.568%   $193.175   $193.18   $193.20   $193.20  
  Purchase #5 $27.68   7.196%   $29.6719   $29.67   $29.65   $29.70  
  Purchase #6 $162.55   4.672%   $170.1443   $170.14   $170.15   $170.10  
  Purchase #7 $33.95   6.241%   $36.0688   $36.07   $36.05   $36.10  
  7 purchase totals = $880.29       $952.1477   $952.16   $952.15   $952.20