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 $236.62   10.638%   $261.7916   $261.79   $261.80   $261.80  
  Purchase #2 $110.31   8.386%   $119.5606   $119.56   $119.55   $119.60  
  Purchase #3 $87.86   12.517%   $98.8574   $98.86   $98.85   $98.90  
  Purchase #4 $173.52   5.347%   $182.7981   $182.80   $182.80   $182.80  
  Purchase #5 $75.54   3.116%   $77.8938   $77.89   $77.90   $77.90  
  Purchase #6 $164.70   5.287%   $173.4077   $173.41   $173.40   $173.40  
  Purchase #7 $187.50   13.716%   $213.2175   $213.22   $213.20   $213.20  
  7 purchase totals = $1,036.05       $1,127.5267   $1,127.53   $1,127.50   $1,127.60