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 $237.67   12.874%   $268.2676   $268.27   $268.25   $268.30  
  Purchase #2 $58.65   13.614%   $66.6346   $66.63   $66.65   $66.60  
  Purchase #3 $99.59   6.726%   $106.2884   $106.29   $106.30   $106.30  
  Purchase #4 $166.59   11.498%   $185.7445   $185.74   $185.75   $185.70  
  Purchase #5 $205.99   4.821%   $215.9208   $215.92   $215.90   $215.90  
  Purchase #6 $105.48   9.553%   $115.5565   $115.56   $115.55   $115.60  
  Purchase #7 $124.77   8.681%   $135.6013   $135.60   $135.60   $135.60  
  7 purchase totals = $998.74       $1,094.0137   $1,094.01   $1,094.00   $1,094.00