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 $91.87   4.693%   $96.1815   $96.18   $96.20   $96.20  
  Purchase #2 $207.59   7.474%   $223.1053   $223.11   $223.10   $223.10  
  Purchase #3 $237.85   6.409%   $253.0938   $253.09   $253.10   $253.10  
  Purchase #4 $29.30   5.230%   $30.8324   $30.83   $30.85   $30.80  
  Purchase #5 $53.90   9.824%   $59.1951   $59.20   $59.20   $59.20  
  Purchase #6 $38.53   5.210%   $40.5374   $40.54   $40.55   $40.50  
  Purchase #7 $52.68   8.230%   $57.0156   $57.02   $57.00   $57.00  
  7 purchase totals = $711.72       $759.9611   $759.97   $760.00   $759.90