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 $138.30   10.390%   $152.6694   $152.67   $152.65   $152.70  
  Purchase #2 $68.84   3.489%   $71.2418   $71.24   $71.25   $71.20  
  Purchase #3 $117.37   7.279%   $125.9134   $125.91   $125.90   $125.90  
  Purchase #4 $147.83   8.172%   $159.9107   $159.91   $159.90   $159.90  
  Purchase #5 $90.42   4.231%   $94.2457   $94.25   $94.25   $94.20  
  Purchase #6 $203.41   5.265%   $214.1195   $214.12   $214.10   $214.10  
  Purchase #7 $132.98   8.669%   $144.508   $144.51   $144.50   $144.50  
  7 purchase totals = $899.15       $962.6085   $962.61   $962.55   $962.50