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 $161.41   3.491%   $167.0448   $167.04   $167.05   $167.00  
  Purchase #2 $60.62   9.606%   $66.4432   $66.44   $66.45   $66.40  
  Purchase #3 $232.81   11.750%   $260.1652   $260.17   $260.15   $260.20  
  Purchase #4 $200.88   9.659%   $220.283   $220.28   $220.30   $220.30  
  Purchase #5 $169.49   6.359%   $180.2679   $180.27   $180.25   $180.30  
  Purchase #6 $179.57   5.182%   $188.8753   $188.88   $188.90   $188.90  
  Purchase #7 $66.90   12.120%   $75.0083   $75.01   $75.00   $75.00  
  7 purchase totals = $1,071.68       $1,158.0877   $1,158.09   $1,158.10   $1,158.10