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 $39.96   4.547%   $41.777   $41.78   $41.80   $41.80  
  Purchase #2 $146.46   11.681%   $163.568   $163.57   $163.55   $163.60  
  Purchase #3 $88.72   9.420%   $97.0774   $97.08   $97.10   $97.10  
  Purchase #4 $244.77   8.800%   $266.3098   $266.31   $266.30   $266.30  
  Purchase #5 $226.76   4.773%   $237.5833   $237.58   $237.60   $237.60  
  Purchase #6 $112.75   10.186%   $124.2347   $124.23   $124.25   $124.20  
  Purchase #7 $91.37   5.382%   $96.2875   $96.29   $96.30   $96.30  
  7 purchase totals = $950.79       $1,026.8377   $1,026.84   $1,026.90   $1,026.90