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 $93.36   5.380%   $98.3828   $98.38   $98.40   $98.40  
  Purchase #2 $221.77   11.750%   $247.828   $247.83   $247.85   $247.80  
  Purchase #3 $85.88   3.300%   $88.714   $88.71   $88.70   $88.70  
  Purchase #4 $157.86   7.643%   $169.9252   $169.93   $169.95   $169.90  
  Purchase #5 $212.35   6.304%   $225.7365   $225.74   $225.75   $225.70  
  Purchase #6 $249.80   12.324%   $280.5854   $280.59   $280.60   $280.60  
  Purchase #7 $60.34   5.123%   $63.4312   $63.43   $63.45   $63.40  
  7 purchase totals = $1,081.36       $1,174.6031   $1,174.61   $1,174.70   $1,174.50