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 $55.92   7.547%   $60.1403   $60.14   $60.15   $60.10  
  Purchase #2 $64.69   3.615%   $67.0285   $67.03   $67.05   $67.00  
  Purchase #3 $232.92   5.541%   $245.8261   $245.83   $245.85   $245.80  
  Purchase #4 $64.84   6.569%   $69.0993   $69.10   $69.10   $69.10  
  Purchase #5 $119.67   6.292%   $127.1996   $127.20   $127.20   $127.20  
  Purchase #6 $25.86   9.602%   $28.3431   $28.34   $28.35   $28.30  
  Purchase #7 $165.79   3.309%   $171.276   $171.28   $171.30   $171.30  
  7 purchase totals = $729.69       $768.9129   $768.92   $769.00   $768.80