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 $21.96   6.256%   $23.3338   $23.33   $23.35   $23.30  
  Purchase #2 $172.40   10.701%   $190.8485   $190.85   $190.85   $190.80  
  Purchase #3 $55.93   10.486%   $61.7948   $61.79   $61.80   $61.80  
  Purchase #4 $125.78   6.719%   $134.2312   $134.23   $134.25   $134.20  
  Purchase #5 $172.57   13.517%   $195.8963   $195.90   $195.90   $195.90  
  Purchase #6 $228.44   5.829%   $241.7558   $241.76   $241.75   $241.80  
  Purchase #7 $106.68   5.426%   $112.4685   $112.47   $112.45   $112.50  
  7 purchase totals = $883.76       $960.3289   $960.33   $960.35   $960.30