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 $205.88   6.474%   $219.2087   $219.21   $219.20   $219.20  
  Purchase #2 $66.25   13.670%   $75.3064   $75.31   $75.30   $75.30  
  Purchase #3 $182.67   7.859%   $197.026   $197.03   $197.05   $197.00  
  Purchase #4 $50.37   4.151%   $52.4609   $52.46   $52.45   $52.50  
  Purchase #5 $7.62   11.627%   $8.506   $8.51   $8.50   $8.50  
  Purchase #6 $226.62   3.809%   $235.252   $235.25   $235.25   $235.30  
  Purchase #7 $71.64   8.271%   $77.5653   $77.57   $77.55   $77.60  
  7 purchase totals = $811.05       $865.3253   $865.34   $865.30   $865.40