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 $192.49   12.746%   $217.0248   $217.02   $217.00   $217.00  
  Purchase #2 $41.55   9.517%   $45.5043   $45.50   $45.50   $45.50  
  Purchase #3 $166.55   7.319%   $178.7398   $178.74   $178.75   $178.70  
  Purchase #4 $136.27   6.202%   $144.7215   $144.72   $144.70   $144.70  
  Purchase #5 $206.49   5.278%   $217.3885   $217.39   $217.40   $217.40  
  Purchase #6 $13.52   6.563%   $14.4073   $14.41   $14.40   $14.40  
  Purchase #7 $122.55   6.198%   $130.1456   $130.15   $130.15   $130.10  
  7 purchase totals = $879.42       $947.9318   $947.93   $947.90   $947.80