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 $246.87   10.196%   $272.0409   $272.04   $272.05   $272.00  
  Purchase #2 $167.73   10.147%   $184.7496   $184.75   $184.75   $184.70  
  Purchase #3 $153.50   4.200%   $159.947   $159.95   $159.95   $159.90  
  Purchase #4 $73.40   12.842%   $82.826   $82.83   $82.85   $82.80  
  Purchase #5 $132.36   9.354%   $144.741   $144.74   $144.75   $144.70  
  Purchase #6 $56.87   7.256%   $60.9965   $61.00   $61.00   $61.00  
  Purchase #7 $180.75   9.158%   $197.3031   $197.30   $197.30   $197.30  
  7 purchase totals = $1,011.48       $1,102.6041   $1,102.61   $1,102.65   $1,102.40