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 $244.45   4.621%   $255.746   $255.75   $255.75   $255.70  
  Purchase #2 $175.28   7.551%   $188.5154   $188.52   $188.50   $188.50  
  Purchase #3 $144.33   12.437%   $162.2803   $162.28   $162.30   $162.30  
  Purchase #4 $104.58   7.832%   $112.7707   $112.77   $112.75   $112.80  
  Purchase #5 $102.89   9.703%   $112.8734   $112.87   $112.85   $112.90  
  Purchase #6 $206.34   8.572%   $224.0275   $224.03   $224.05   $224.00  
  Purchase #7 $164.80   12.261%   $185.0061   $185.01   $185.00   $185.00  
  7 purchase totals = $1,142.67       $1,241.2194   $1,241.23   $1,241.20   $1,241.20