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 $179.61   9.745%   $197.113   $197.11   $197.10   $197.10  
  Purchase #2 $157.56   10.199%   $173.6295   $173.63   $173.65   $173.60  
  Purchase #3 $204.27   9.636%   $223.9535   $223.95   $223.95   $224.00  
  Purchase #4 $247.67   6.756%   $264.4026   $264.40   $264.40   $264.40  
  Purchase #5 $7.30   4.422%   $7.6228   $7.62   $7.60   $7.60  
  Purchase #6 $138.68   4.194%   $144.4962   $144.50   $144.50   $144.50  
  Purchase #7 $232.58   13.378%   $263.6946   $263.69   $263.70   $263.70  
  7 purchase totals = $1,167.67       $1,274.9122   $1,274.90   $1,274.90   $1,274.90