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 $24.98   5.785%   $26.4251   $26.43   $26.45   $26.40  
  Purchase #2 $135.43   6.265%   $143.9147   $143.91   $143.90   $143.90  
  Purchase #3 $169.77   11.571%   $189.4141   $189.41   $189.40   $189.40  
  Purchase #4 $109.29   3.569%   $113.1906   $113.19   $113.20   $113.20  
  Purchase #5 $5.45   7.322%   $5.849   $5.85   $5.85   $5.80  
  Purchase #6 $128.63   6.218%   $136.6282   $136.63   $136.65   $136.60  
  Purchase #7 $232.69   6.126%   $246.9446   $246.94   $246.95   $246.90  
  7 purchase totals = $806.24       $862.3663   $862.36   $862.40   $862.20