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 $60.80   8.644%   $66.0556   $66.06   $66.05   $66.10  
  Purchase #2 $222.46   10.473%   $245.7582   $245.76   $245.75   $245.80  
  Purchase #3 $170.63   9.175%   $186.2853   $186.29   $186.30   $186.30  
  Purchase #4 $213.58   4.835%   $223.9066   $223.91   $223.90   $223.90  
  Purchase #5 $217.63   4.651%   $227.752   $227.75   $227.75   $227.80  
  Purchase #6 $209.52   3.626%   $217.1172   $217.12   $217.10   $217.10  
  Purchase #7 $140.67   12.666%   $158.4873   $158.49   $158.50   $158.50  
  7 purchase totals = $1,235.29       $1,325.3622   $1,325.38   $1,325.35   $1,325.50