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 $61.61   12.134%   $69.0858   $69.09   $69.10   $69.10  
  Purchase #2 $162.59   13.759%   $184.9608   $184.96   $184.95   $185.00  
  Purchase #3 $214.40   10.714%   $237.3708   $237.37   $237.35   $237.40  
  Purchase #4 $50.45   11.259%   $56.1302   $56.13   $56.15   $56.10  
  Purchase #5 $14.48   11.812%   $16.1904   $16.19   $16.20   $16.20  
  Purchase #6 $34.83   9.205%   $38.0361   $38.04   $38.05   $38.00  
  Purchase #7 $165.46   8.694%   $179.8451   $179.85   $179.85   $179.80  
  7 purchase totals = $703.82       $781.6192   $781.63   $781.65   $781.60