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 $165.57   4.848%   $173.5968   $173.60   $173.60   $173.60  
  Purchase #2 $131.93   11.248%   $146.7695   $146.77   $146.75   $146.80  
  Purchase #3 $205.69   8.137%   $222.427   $222.43   $222.45   $222.40  
  Purchase #4 $164.58   4.277%   $171.6191   $171.62   $171.60   $171.60  
  Purchase #5 $212.96   5.607%   $224.9007   $224.90   $224.90   $224.90  
  Purchase #6 $38.44   6.779%   $41.0458   $41.05   $41.05   $41.00  
  Purchase #7 $10.27   9.461%   $11.2416   $11.24   $11.25   $11.20  
  7 purchase totals = $929.44       $991.6005   $991.61   $991.60   $991.50