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 $110.68   6.719%   $118.1166   $118.12   $118.10   $118.10  
  Purchase #2 $238.67   13.687%   $271.3368   $271.34   $271.35   $271.30  
  Purchase #3 $209.43   6.230%   $222.4775   $222.48   $222.50   $222.50  
  Purchase #4 $139.71   6.260%   $148.4558   $148.46   $148.45   $148.50  
  Purchase #5 $197.63   3.329%   $204.2091   $204.21   $204.20   $204.20  
  Purchase #6 $219.88   11.467%   $245.0936   $245.09   $245.10   $245.10  
  Purchase #7 $52.27   7.404%   $56.1401   $56.14   $56.15   $56.10  
  7 purchase totals = $1,168.27       $1,265.8295   $1,265.84   $1,265.85   $1,265.80