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 $90.36   11.709%   $100.9403   $100.94   $100.95   $100.90  
  Purchase #2 $38.95   7.133%   $41.7283   $41.73   $41.75   $41.70  
  Purchase #3 $195.72   9.766%   $214.834   $214.83   $214.85   $214.80  
  Purchase #4 $48.88   5.361%   $51.5005   $51.50   $51.50   $51.50  
  Purchase #5 $156.62   8.235%   $169.5177   $169.52   $169.50   $169.50  
  Purchase #6 $202.68   11.507%   $226.0024   $226.00   $226.00   $226.00  
  Purchase #7 $188.69   9.369%   $206.3684   $206.37   $206.35   $206.40  
  7 purchase totals = $921.90       $1,010.8916   $1,010.89   $1,010.90   $1,010.80