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 $65.93   4.137%   $68.6575   $68.66   $68.65   $68.70  
  Purchase #2 $147.61   11.728%   $164.9217   $164.92   $164.90   $164.90  
  Purchase #3 $6.42   12.277%   $7.2082   $7.21   $7.20   $7.20  
  Purchase #4 $225.30   8.221%   $243.8219   $243.82   $243.80   $243.80  
  Purchase #5 $159.90   9.256%   $174.7003   $174.70   $174.70   $174.70  
  Purchase #6 $47.87   3.305%   $49.4521   $49.45   $49.45   $49.50  
  Purchase #7 $22.89   3.828%   $23.7662   $23.77   $23.75   $23.80  
  7 purchase totals = $675.92       $732.5279   $732.53   $732.45   $732.60