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 $189.96   10.143%   $209.2276   $209.23   $209.25   $209.20  
  Purchase #2 $103.38   13.552%   $117.3901   $117.39   $117.40   $117.40  
  Purchase #3 $184.57   8.208%   $199.7195   $199.72   $199.70   $199.70  
  Purchase #4 $132.77   7.612%   $142.8765   $142.88   $142.90   $142.90  
  Purchase #5 $240.87   11.536%   $268.6568   $268.66   $268.65   $268.70  
  Purchase #6 $54.97   13.159%   $62.2035   $62.20   $62.20   $62.20  
  Purchase #7 $90.90   3.186%   $93.7961   $93.80   $93.80   $93.80  
  7 purchase totals = $997.42       $1,093.8701   $1,093.88   $1,093.90   $1,093.90