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 $208.44   11.580%   $232.5774   $232.58   $232.60   $232.60  
  Purchase #2 $124.81   5.286%   $131.4075   $131.41   $131.40   $131.40  
  Purchase #3 $129.31   5.435%   $136.338   $136.34   $136.35   $136.30  
  Purchase #4 $87.98   13.397%   $99.7667   $99.77   $99.75   $99.80  
  Purchase #5 $199.84   12.482%   $224.784   $224.78   $224.80   $224.80  
  Purchase #6 $150.57   11.328%   $167.6266   $167.63   $167.65   $167.60  
  Purchase #7 $239.31   4.266%   $249.519   $249.52   $249.50   $249.50  
  7 purchase totals = $1,140.26       $1,242.0192   $1,242.03   $1,242.05   $1,242.00