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 $205.78   13.548%   $233.6591   $233.66   $233.65   $233.70  
  Purchase #2 $32.79   10.249%   $36.1506   $36.15   $36.15   $36.20  
  Purchase #3 $155.63   3.817%   $161.5704   $161.57   $161.55   $161.60  
  Purchase #4 $85.26   9.466%   $93.3307   $93.33   $93.35   $93.30  
  Purchase #5 $115.57   5.801%   $122.2742   $122.27   $122.25   $122.30  
  Purchase #6 $57.28   6.850%   $61.2037   $61.20   $61.20   $61.20  
  Purchase #7 $137.40   8.815%   $149.5118   $149.51   $149.50   $149.50  
  7 purchase totals = $789.71       $857.7005   $857.69   $857.65   $857.80