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 $242.64   13.714%   $275.9156   $275.92   $275.90   $275.90  
  Purchase #2 $242.56   10.838%   $268.8487   $268.85   $268.85   $268.80  
  Purchase #3 $234.96   4.657%   $245.9021   $245.90   $245.90   $245.90  
  Purchase #4 $67.96   4.209%   $70.8204   $70.82   $70.80   $70.80  
  Purchase #5 $148.81   5.862%   $157.5332   $157.53   $157.55   $157.50  
  Purchase #6 $14.30   3.175%   $14.754   $14.75   $14.75   $14.80  
  Purchase #7 $108.64   4.590%   $113.6266   $113.63   $113.65   $113.60  
  7 purchase totals = $1,059.87       $1,147.4006   $1,147.40   $1,147.40   $1,147.30