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 $221.59   11.841%   $247.8285   $247.83   $247.85   $247.80  
  Purchase #2 $234.95   13.790%   $267.3496   $267.35   $267.35   $267.30  
  Purchase #3 $225.81   8.576%   $245.1755   $245.18   $245.20   $245.20  
  Purchase #4 $149.49   6.221%   $158.7898   $158.79   $158.80   $158.80  
  Purchase #5 $185.81   11.566%   $207.3008   $207.30   $207.30   $207.30  
  Purchase #6 $82.28   4.760%   $86.1965   $86.20   $86.20   $86.20  
  Purchase #7 $28.85   4.359%   $30.1076   $30.11   $30.10   $30.10  
  7 purchase totals = $1,128.78       $1,242.7483   $1,242.76   $1,242.80   $1,242.70