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 $244.65   8.219%   $264.7578   $264.76   $264.75   $264.80  
  Purchase #2 $112.85   4.166%   $117.5513   $117.55   $117.55   $117.60  
  Purchase #3 $244.71   12.205%   $274.5769   $274.58   $274.60   $274.60  
  Purchase #4 $68.26   7.790%   $73.5775   $73.58   $73.60   $73.60  
  Purchase #5 $162.93   8.548%   $176.8573   $176.86   $176.85   $176.90  
  Purchase #6 $13.70   11.761%   $15.3113   $15.31   $15.30   $15.30  
  Purchase #7 $129.93   5.590%   $137.1931   $137.19   $137.20   $137.20  
  7 purchase totals = $977.03       $1,059.8252   $1,059.83   $1,059.85   $1,060.00