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 $188.57   3.265%   $194.7268   $194.73   $194.75   $194.70  
  Purchase #2 $242.76   12.598%   $273.3429   $273.34   $273.35   $273.30  
  Purchase #3 $184.73   5.721%   $195.2984   $195.30   $195.30   $195.30  
  Purchase #4 $164.55   13.211%   $186.2887   $186.29   $186.30   $186.30  
  Purchase #5 $223.89   12.746%   $252.427   $252.43   $252.45   $252.40  
  Purchase #6 $17.37   5.404%   $18.3087   $18.31   $18.30   $18.30  
  Purchase #7 $247.38   6.837%   $264.2934   $264.29   $264.30   $264.30  
  7 purchase totals = $1,269.25       $1,384.6859   $1,384.69   $1,384.75   $1,384.60