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 $22.42   10.233%   $24.7142   $24.71   $24.70   $24.70  
  Purchase #2 $226.51   11.784%   $253.2019   $253.20   $253.20   $253.20  
  Purchase #3 $126.66   6.588%   $135.0044   $135.00   $135.00   $135.00  
  Purchase #4 $85.81   12.310%   $96.3732   $96.37   $96.35   $96.40  
  Purchase #5 $201.33   10.483%   $222.4354   $222.44   $222.45   $222.40  
  Purchase #6 $111.28   12.783%   $125.5049   $125.50   $125.50   $125.50  
  Purchase #7 $198.78   3.480%   $205.6975   $205.70   $205.70   $205.70  
  7 purchase totals = $972.79       $1,062.9315   $1,062.92   $1,062.90   $1,062.90