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 $56.63   13.345%   $64.1873   $64.19   $64.20   $64.20  
  Purchase #2 $230.42   4.247%   $240.2059   $240.21   $240.20   $240.20  
  Purchase #3 $83.47   5.272%   $87.8705   $87.87   $87.85   $87.90  
  Purchase #4 $233.83   13.228%   $264.761   $264.76   $264.75   $264.80  
  Purchase #5 $27.76   4.802%   $29.093   $29.09   $29.10   $29.10  
  Purchase #6 $45.70   7.232%   $49.005   $49.01   $49.00   $49.00  
  Purchase #7 $207.26   11.830%   $231.7789   $231.78   $231.80   $231.80  
  7 purchase totals = $885.07       $966.9016   $966.91   $966.90   $967.00