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 $231.93   11.388%   $258.3422   $258.34   $258.35   $258.30  
  Purchase #2 $220.91   10.840%   $244.8566   $244.86   $244.85   $244.90  
  Purchase #3 $71.74   4.617%   $75.0522   $75.05   $75.05   $75.10  
  Purchase #4 $202.33   10.846%   $224.2747   $224.27   $224.25   $224.30  
  Purchase #5 $151.33   6.124%   $160.5974   $160.60   $160.60   $160.60  
  Purchase #6 $113.64   9.430%   $124.3563   $124.36   $124.35   $124.40  
  Purchase #7 $222.43   9.675%   $243.9501   $243.95   $243.95   $244.00  
  7 purchase totals = $1,214.31       $1,331.4295   $1,331.43   $1,331.40   $1,331.60