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 $63.87   13.567%   $72.5352   $72.54   $72.55   $72.50  
  Purchase #2 $77.82   10.742%   $86.1794   $86.18   $86.20   $86.20  
  Purchase #3 $174.47   13.486%   $197.999   $198.00   $198.00   $198.00  
  Purchase #4 $85.79   3.388%   $88.6966   $88.70   $88.70   $88.70  
  Purchase #5 $71.76   3.145%   $74.0169   $74.02   $74.00   $74.00  
  Purchase #6 $195.89   3.357%   $202.466   $202.47   $202.45   $202.50  
  Purchase #7 $57.88   4.437%   $60.4481   $60.45   $60.45   $60.40  
  7 purchase totals = $727.48       $782.3412   $782.36   $782.35   $782.30