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 $24.44   3.114%   $25.2011   $25.20   $25.20   $25.20  
  Purchase #2 $35.46   11.706%   $39.6109   $39.61   $39.60   $39.60  
  Purchase #3 $112.77   4.492%   $117.8356   $117.84   $117.85   $117.80  
  Purchase #4 $244.50   4.694%   $255.9768   $255.98   $256.00   $256.00  
  Purchase #5 $112.56   4.239%   $117.3314   $117.33   $117.35   $117.30  
  Purchase #6 $100.34   6.373%   $106.7347   $106.73   $106.75   $106.70  
  Purchase #7 $119.62   12.591%   $134.6814   $134.68   $134.70   $134.70  
  7 purchase totals = $749.69       $797.3719   $797.37   $797.45   $797.30