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 $235.45   13.384%   $266.9626   $266.96   $266.95   $267.00  
  Purchase #2 $148.76   12.717%   $167.6778   $167.68   $167.70   $167.70  
  Purchase #3 $116.40   5.439%   $122.731   $122.73   $122.75   $122.70  
  Purchase #4 $249.75   6.317%   $265.5267   $265.53   $265.55   $265.50  
  Purchase #5 $55.93   5.380%   $58.939   $58.94   $58.95   $58.90  
  Purchase #6 $158.52   9.402%   $173.4241   $173.42   $173.40   $173.40  
  Purchase #7 $241.98   3.464%   $250.3622   $250.36   $250.35   $250.40  
  7 purchase totals = $1,206.79       $1,305.6234   $1,305.62   $1,305.65   $1,305.60