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 $33.73   6.792%   $36.0209   $36.02   $36.00   $36.00  
  Purchase #2 $195.65   6.555%   $208.4749   $208.47   $208.45   $208.50  
  Purchase #3 $236.41   13.624%   $268.6185   $268.62   $268.60   $268.60  
  Purchase #4 $183.72   7.660%   $197.793   $197.79   $197.80   $197.80  
  Purchase #5 $97.93   11.805%   $109.4906   $109.49   $109.50   $109.50  
  Purchase #6 $57.49   6.703%   $61.3436   $61.34   $61.35   $61.30  
  Purchase #7 $11.96   3.573%   $12.3873   $12.39   $12.40   $12.40  
  7 purchase totals = $816.89       $894.1288   $894.12   $894.10   $894.10