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 $126.76   6.539%   $135.0488   $135.05   $135.05   $135.00  
  Purchase #2 $60.56   10.203%   $66.7389   $66.74   $66.75   $66.70  
  Purchase #3 $70.80   4.857%   $74.2388   $74.24   $74.25   $74.20  
  Purchase #4 $15.60   9.789%   $17.1271   $17.13   $17.15   $17.10  
  Purchase #5 $226.71   6.107%   $240.5552   $240.56   $240.55   $240.60  
  Purchase #6 $55.85   5.117%   $58.7078   $58.71   $58.70   $58.70  
  Purchase #7 $243.52   7.494%   $261.7694   $261.77   $261.75   $261.80  
  7 purchase totals = $799.80       $854.1860   $854.20   $854.20   $854.10