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 $194.93   13.851%   $221.9298   $221.93   $221.95   $221.90  
  Purchase #2 $14.37   6.244%   $15.2673   $15.27   $15.25   $15.30  
  Purchase #3 $130.97   9.360%   $143.2288   $143.23   $143.25   $143.20  
  Purchase #4 $92.77   6.262%   $98.5793   $98.58   $98.60   $98.60  
  Purchase #5 $97.96   4.665%   $102.5298   $102.53   $102.55   $102.50  
  Purchase #6 $96.62   3.319%   $99.8268   $99.83   $99.85   $99.80  
  Purchase #7 $241.46   13.255%   $273.4655   $273.47   $273.45   $273.50  
  7 purchase totals = $869.08       $954.8273   $954.84   $954.90   $954.80