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 $206.39   13.282%   $233.8027   $233.80   $233.80   $233.80  
  Purchase #2 $213.40   5.434%   $224.9962   $225.00   $225.00   $225.00  
  Purchase #3 $161.42   9.500%   $176.7549   $176.75   $176.75   $176.80  
  Purchase #4 $72.63   3.702%   $75.3188   $75.32   $75.30   $75.30  
  Purchase #5 $120.96   5.690%   $127.8426   $127.84   $127.85   $127.80  
  Purchase #6 $37.87   11.635%   $42.2762   $42.28   $42.30   $42.30  
  Purchase #7 $119.41   9.547%   $130.8101   $130.81   $130.80   $130.80  
  7 purchase totals = $932.08       $1,011.8015   $1,011.80   $1,011.80   $1,011.80