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 $45.86   10.587%   $50.7152   $50.72   $50.70   $50.70  
  Purchase #2 $171.37   5.426%   $180.6685   $180.67   $180.65   $180.70  
  Purchase #3 $247.41   11.868%   $276.7726   $276.77   $276.75   $276.80  
  Purchase #4 $32.77   11.769%   $36.6267   $36.63   $36.65   $36.60  
  Purchase #5 $60.46   12.853%   $68.2309   $68.23   $68.25   $68.20  
  Purchase #6 $117.53   11.239%   $130.7392   $130.74   $130.75   $130.70  
  Purchase #7 $106.94   8.496%   $116.0256   $116.03   $116.05   $116.00  
  7 purchase totals = $782.34       $859.7787   $859.79   $859.80   $859.70