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 $113.64   8.104%   $122.8494   $122.85   $122.85   $122.80  
  Purchase #2 $182.35   5.391%   $192.1805   $192.18   $192.20   $192.20  
  Purchase #3 $237.80   9.863%   $261.2542   $261.25   $261.25   $261.30  
  Purchase #4 $50.58   9.383%   $55.3259   $55.33   $55.35   $55.30  
  Purchase #5 $83.59   6.370%   $88.9147   $88.91   $88.90   $88.90  
  Purchase #6 $60.26   7.417%   $64.7295   $64.73   $64.75   $64.70  
  Purchase #7 $248.27   5.534%   $262.0093   $262.01   $262.00   $262.00  
  7 purchase totals = $976.49       $1,047.2635   $1,047.26   $1,047.30   $1,047.20