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 $227.80   8.299%   $246.7051   $246.71   $246.70   $246.70  
  Purchase #2 $174.46   11.601%   $194.6991   $194.70   $194.70   $194.70  
  Purchase #3 $175.71   12.782%   $198.1693   $198.17   $198.15   $198.20  
  Purchase #4 $245.87   9.284%   $268.6966   $268.70   $268.70   $268.70  
  Purchase #5 $70.36   11.251%   $78.2762   $78.28   $78.30   $78.30  
  Purchase #6 $166.64   5.368%   $175.5852   $175.59   $175.60   $175.60  
  Purchase #7 $195.79   6.393%   $208.3069   $208.31   $208.30   $208.30  
  7 purchase totals = $1,256.63       $1,370.4384   $1,370.46   $1,370.45   $1,370.50