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 $54.37   12.105%   $60.9515   $60.95   $60.95   $61.00  
  Purchase #2 $95.78   8.372%   $103.7987   $103.80   $103.80   $103.80  
  Purchase #3 $180.72   7.642%   $194.5306   $194.53   $194.55   $194.50  
  Purchase #4 $119.74   6.296%   $127.2788   $127.28   $127.30   $127.30  
  Purchase #5 $102.25   12.720%   $115.2562   $115.26   $115.25   $115.30  
  Purchase #6 $140.41   3.444%   $145.2457   $145.25   $145.25   $145.20  
  Purchase #7 $113.65   3.238%   $117.33   $117.33   $117.35   $117.30  
  7 purchase totals = $806.92       $864.3915   $864.40   $864.45   $864.40