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 $218.44   11.408%   $243.3596   $243.36   $243.35   $243.40  
  Purchase #2 $165.83   12.469%   $186.5073   $186.51   $186.50   $186.50  
  Purchase #3 $210.98   12.457%   $237.2618   $237.26   $237.25   $237.30  
  Purchase #4 $160.65   4.614%   $168.0624   $168.06   $168.05   $168.10  
  Purchase #5 $229.44   5.343%   $241.699   $241.70   $241.70   $241.70  
  Purchase #6 $200.54   10.298%   $221.1916   $221.19   $221.20   $221.20  
  Purchase #7 $177.75   6.105%   $188.6016   $188.60   $188.60   $188.60  
  7 purchase totals = $1,363.63       $1,486.6833   $1,486.68   $1,486.65   $1,486.80