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 $244.78   6.696%   $261.1705   $261.17   $261.15   $261.20  
  Purchase #2 $62.54   4.324%   $65.2442   $65.24   $65.25   $65.20  
  Purchase #3 $224.44   5.384%   $236.5238   $236.52   $236.50   $236.50  
  Purchase #4 $53.98   9.233%   $58.964   $58.96   $58.95   $59.00  
  Purchase #5 $77.72   9.864%   $85.3863   $85.39   $85.40   $85.40  
  Purchase #6 $220.47   7.516%   $237.0405   $237.04   $237.05   $237.00  
  Purchase #7 $165.25   12.235%   $185.4683   $185.47   $185.45   $185.50  
  7 purchase totals = $1,049.18       $1,129.7976   $1,129.79   $1,129.75   $1,129.80