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 $122.45   12.559%   $137.8285   $137.83   $137.85   $137.80  
  Purchase #2 $175.87   4.436%   $183.6716   $183.67   $183.65   $183.70  
  Purchase #3 $79.65   12.614%   $89.6971   $89.70   $89.70   $89.70  
  Purchase #4 $25.61   6.823%   $27.3574   $27.36   $27.35   $27.40  
  Purchase #5 $103.28   12.629%   $116.3232   $116.32   $116.30   $116.30  
  Purchase #6 $82.77   13.633%   $94.054   $94.05   $94.05   $94.10  
  Purchase #7 $71.82   4.840%   $75.2961   $75.30   $75.30   $75.30  
  7 purchase totals = $661.45       $724.2279   $724.23   $724.20   $724.30