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 $184.31   6.312%   $195.9436   $195.94   $195.95   $195.90  
  Purchase #2 $184.72   3.760%   $191.6655   $191.67   $191.65   $191.70  
  Purchase #3 $46.29   6.618%   $49.3535   $49.35   $49.35   $49.40  
  Purchase #4 $227.72   5.826%   $240.987   $240.99   $241.00   $241.00  
  Purchase #5 $155.81   13.132%   $176.271   $176.27   $176.25   $176.30  
  Purchase #6 $45.43   7.816%   $48.9808   $48.98   $49.00   $49.00  
  Purchase #7 $76.78   9.652%   $84.1908   $84.19   $84.20   $84.20  
  7 purchase totals = $921.06       $987.3922   $987.39   $987.40   $987.50