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 $208.83   8.313%   $226.19   $226.19   $226.20   $226.20  
  Purchase #2 $244.53   8.103%   $264.3443   $264.34   $264.35   $264.30  
  Purchase #3 $237.90   3.578%   $246.4121   $246.41   $246.40   $246.40  
  Purchase #4 $56.42   12.192%   $63.2987   $63.30   $63.30   $63.30  
  Purchase #5 $113.42   4.205%   $118.1893   $118.19   $118.20   $118.20  
  Purchase #6 $64.99   9.564%   $71.2056   $71.21   $71.20   $71.20  
  Purchase #7 $18.41   8.851%   $20.0395   $20.04   $20.05   $20.00  
  7 purchase totals = $944.50       $1,009.6795   $1,009.68   $1,009.70   $1,009.60