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 $232.81   10.562%   $257.3994   $257.40   $257.40   $257.40  
  Purchase #2 $168.91   9.332%   $184.6727   $184.67   $184.65   $184.70  
  Purchase #3 $159.90   4.295%   $166.7677   $166.77   $166.75   $166.80  
  Purchase #4 $119.91   8.743%   $130.3937   $130.39   $130.40   $130.40  
  Purchase #5 $118.26   10.453%   $130.6217   $130.62   $130.60   $130.60  
  Purchase #6 $237.79   12.300%   $267.0382   $267.04   $267.05   $267.00  
  Purchase #7 $23.77   5.582%   $25.0968   $25.10   $25.10   $25.10  
  7 purchase totals = $1,061.35       $1,161.9902   $1,161.99   $1,161.95   $1,162.00