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 $56.87   6.597%   $60.6217   $60.62   $60.60   $60.60  
  Purchase #2 $120.76   3.603%   $125.111   $125.11   $125.10   $125.10  
  Purchase #3 $243.85   7.335%   $261.7364   $261.74   $261.75   $261.70  
  Purchase #4 $150.27   12.527%   $169.0943   $169.09   $169.10   $169.10  
  Purchase #5 $114.49   4.373%   $119.4966   $119.50   $119.50   $119.50  
  Purchase #6 $160.64   4.328%   $167.5925   $167.59   $167.60   $167.60  
  Purchase #7 $94.40   11.300%   $105.0672   $105.07   $105.05   $105.10  
  7 purchase totals = $941.28       $1,008.7197   $1,008.72   $1,008.70   $1,008.70