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 $206.98   9.503%   $226.6493   $226.65   $226.65   $226.60  
  Purchase #2 $119.77   13.835%   $136.3402   $136.34   $136.35   $136.30  
  Purchase #3 $182.43   6.561%   $194.3992   $194.40   $194.40   $194.40  
  Purchase #4 $125.94   8.591%   $136.7595   $136.76   $136.75   $136.80  
  Purchase #5 $181.89   6.800%   $194.2585   $194.26   $194.25   $194.30  
  Purchase #6 $150.71   8.549%   $163.5942   $163.59   $163.60   $163.60  
  Purchase #7 $226.88   3.175%   $234.0834   $234.08   $234.10   $234.10  
  7 purchase totals = $1,194.60       $1,286.0843   $1,286.08   $1,286.10   $1,286.10