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 $33.58   9.241%   $36.6831   $36.68   $36.70   $36.70  
  Purchase #2 $158.54   9.502%   $173.6045   $173.60   $173.60   $173.60  
  Purchase #3 $60.68   3.583%   $62.8542   $62.85   $62.85   $62.90  
  Purchase #4 $131.44   7.323%   $141.0654   $141.07   $141.05   $141.10  
  Purchase #5 $166.97   8.853%   $181.7519   $181.75   $181.75   $181.80  
  Purchase #6 $23.33   4.763%   $24.4412   $24.44   $24.45   $24.40  
  Purchase #7 $204.44   6.780%   $218.301   $218.30   $218.30   $218.30  
  7 purchase totals = $778.98       $838.7013   $838.69   $838.70   $838.80