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 $187.77   9.622%   $205.8372   $205.84   $205.85   $205.80  
  Purchase #2 $62.88   4.135%   $65.4801   $65.48   $65.50   $65.50  
  Purchase #3 $235.52   9.346%   $257.5317   $257.53   $257.55   $257.50  
  Purchase #4 $131.57   5.390%   $138.6616   $138.66   $138.65   $138.70  
  Purchase #5 $157.44   9.470%   $172.3496   $172.35   $172.35   $172.30  
  Purchase #6 $32.90   10.800%   $36.4532   $36.45   $36.45   $36.50  
  Purchase #7 $126.71   8.613%   $137.6235   $137.62   $137.60   $137.60  
  7 purchase totals = $934.79       $1,013.9369   $1,013.93   $1,013.95   $1,013.90