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 $69.62   9.362%   $76.1378   $76.14   $76.15   $76.10  
  Purchase #2 $189.55   12.481%   $213.2077   $213.21   $213.20   $213.20  
  Purchase #3 $31.33   7.585%   $33.7064   $33.71   $33.70   $33.70  
  Purchase #4 $208.29   11.144%   $231.5018   $231.50   $231.50   $231.50  
  Purchase #5 $126.46   5.518%   $133.4381   $133.44   $133.45   $133.40  
  Purchase #6 $169.95   5.312%   $178.9777   $178.98   $179.00   $179.00  
  Purchase #7 $248.50   10.298%   $274.0905   $274.09   $274.10   $274.10  
  7 purchase totals = $1,043.70       $1,141.0600   $1,141.07   $1,141.10   $1,141.00