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 $125.54   8.829%   $136.6239   $136.62   $136.60   $136.60  
  Purchase #2 $222.92   9.738%   $244.6279   $244.63   $244.65   $244.60  
  Purchase #3 $235.72   9.187%   $257.3756   $257.38   $257.40   $257.40  
  Purchase #4 $41.37   5.661%   $43.712   $43.71   $43.70   $43.70  
  Purchase #5 $34.28   5.235%   $36.0746   $36.07   $36.05   $36.10  
  Purchase #6 $62.76   13.713%   $71.3663   $71.37   $71.35   $71.40  
  Purchase #7 $221.28   11.561%   $246.8622   $246.86   $246.85   $246.90  
  7 purchase totals = $943.87       $1,036.6425   $1,036.64   $1,036.60   $1,036.70