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 $239.41   10.773%   $265.2016   $265.20   $265.20   $265.20  
  Purchase #2 $32.89   5.365%   $34.6545   $34.65   $34.65   $34.70  
  Purchase #3 $30.60   8.614%   $33.2359   $33.24   $33.25   $33.20  
  Purchase #4 $217.62   8.272%   $235.6215   $235.62   $235.60   $235.60  
  Purchase #5 $9.70   7.523%   $10.4297   $10.43   $10.45   $10.40  
  Purchase #6 $149.79   11.428%   $166.908   $166.91   $166.90   $166.90  
  Purchase #7 $235.79   9.550%   $258.3079   $258.31   $258.30   $258.30  
  7 purchase totals = $915.80       $1,004.3591   $1,004.36   $1,004.35   $1,004.30