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 $172.90   9.642%   $189.571   $189.57   $189.55   $189.60  
  Purchase #2 $49.41   10.722%   $54.7077   $54.71   $54.70   $54.70  
  Purchase #3 $89.55   6.340%   $95.2275   $95.23   $95.25   $95.20  
  Purchase #4 $169.83   10.666%   $187.9441   $187.94   $187.95   $187.90  
  Purchase #5 $135.51   9.869%   $148.8835   $148.88   $148.90   $148.90  
  Purchase #6 $232.97   10.311%   $256.9915   $256.99   $257.00   $257.00  
  Purchase #7 $234.72   9.544%   $257.1217   $257.12   $257.10   $257.10  
  7 purchase totals = $1,084.89       $1,190.4470   $1,190.44   $1,190.45   $1,190.40