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 $228.32   9.414%   $249.814   $249.81   $249.80   $249.80  
  Purchase #2 $41.28   10.845%   $45.7568   $45.76   $45.75   $45.80  
  Purchase #3 $159.74   8.694%   $173.6278   $173.63   $173.65   $173.60  
  Purchase #4 $66.44   7.534%   $71.4456   $71.45   $71.45   $71.40  
  Purchase #5 $181.69   5.144%   $191.0361   $191.04   $191.05   $191.00  
  Purchase #6 $205.76   10.254%   $226.8586   $226.86   $226.85   $226.90  
  Purchase #7 $23.71   9.701%   $26.0101   $26.01   $26.00   $26.00  
  7 purchase totals = $906.94       $984.5490   $984.56   $984.55   $984.50