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 $241.42   11.650%   $269.5454   $269.55   $269.55   $269.50  
  Purchase #2 $30.89   8.582%   $33.541   $33.54   $33.55   $33.50  
  Purchase #3 $62.53   7.570%   $67.2635   $67.26   $67.25   $67.30  
  Purchase #4 $206.52   8.532%   $224.1403   $224.14   $224.15   $224.10  
  Purchase #5 $112.39   10.653%   $124.3629   $124.36   $124.35   $124.40  
  Purchase #6 $11.37   8.584%   $12.346   $12.35   $12.35   $12.30  
  Purchase #7 $39.82   4.677%   $41.6824   $41.68   $41.70   $41.70  
  7 purchase totals = $704.94       $772.8815   $772.88   $772.90   $772.80