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 $64.31   3.797%   $66.7519   $66.75   $66.75   $66.80  
  Purchase #2 $202.98   5.411%   $213.9632   $213.96   $213.95   $214.00  
  Purchase #3 $136.92   7.826%   $147.6354   $147.64   $147.65   $147.60  
  Purchase #4 $112.67   4.267%   $117.4776   $117.48   $117.50   $117.50  
  Purchase #5 $138.62   4.315%   $144.6015   $144.60   $144.60   $144.60  
  Purchase #6 $151.92   7.243%   $162.9236   $162.92   $162.90   $162.90  
  Purchase #7 $9.93   6.290%   $10.5546   $10.55   $10.55   $10.60  
  7 purchase totals = $817.35       $863.9078   $863.90   $863.90   $864.00