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 $62.27   9.168%   $67.9789   $67.98   $68.00   $68.00  
  Purchase #2 $40.98   6.139%   $43.4958   $43.50   $43.50   $43.50  
  Purchase #3 $181.68   7.858%   $195.9564   $195.96   $195.95   $196.00  
  Purchase #4 $221.31   11.756%   $247.3272   $247.33   $247.35   $247.30  
  Purchase #5 $55.74   11.747%   $62.2878   $62.29   $62.30   $62.30  
  Purchase #6 $157.48   3.340%   $162.7398   $162.74   $162.75   $162.70  
  Purchase #7 $151.60   6.816%   $161.9331   $161.93   $161.95   $161.90  
  7 purchase totals = $871.06       $941.7190   $941.73   $941.80   $941.70