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 $172.35   10.677%   $190.7518   $190.75   $190.75   $190.80  
  Purchase #2 $111.85   5.421%   $117.9134   $117.91   $117.90   $117.90  
  Purchase #3 $111.50   12.356%   $125.2769   $125.28   $125.30   $125.30  
  Purchase #4 $169.73   8.437%   $184.0501   $184.05   $184.05   $184.10  
  Purchase #5 $152.66   13.867%   $173.8294   $173.83   $173.85   $173.80  
  Purchase #6 $193.39   5.347%   $203.7306   $203.73   $203.75   $203.70  
  Purchase #7 $68.74   10.763%   $76.1385   $76.14   $76.15   $76.10  
  7 purchase totals = $980.22       $1,071.6907   $1,071.69   $1,071.75   $1,071.70