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 $52.95   9.296%   $57.8722   $57.87   $57.85   $57.90  
  Purchase #2 $197.69   5.147%   $207.8651   $207.87   $207.85   $207.90  
  Purchase #3 $142.58   12.325%   $160.153   $160.15   $160.15   $160.20  
  Purchase #4 $117.25   12.539%   $131.952   $131.95   $131.95   $132.00  
  Purchase #5 $169.25   10.331%   $186.7352   $186.74   $186.75   $186.70  
  Purchase #6 $182.59   3.854%   $189.627   $189.63   $189.65   $189.60  
  Purchase #7 $76.30   10.598%   $84.3863   $84.39   $84.40   $84.40  
  7 purchase totals = $938.61       $1,018.5908   $1,018.60   $1,018.60   $1,018.70