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 $60.50   7.433%   $64.997   $65.00   $65.00   $65.00  
  Purchase #2 $170.94   4.581%   $178.7708   $178.77   $178.75   $178.80  
  Purchase #3 $33.49   3.604%   $34.697   $34.70   $34.70   $34.70  
  Purchase #4 $87.83   13.283%   $99.4965   $99.50   $99.50   $99.50  
  Purchase #5 $65.60   8.651%   $71.2751   $71.28   $71.30   $71.30  
  Purchase #6 $204.80   4.357%   $213.7231   $213.72   $213.70   $213.70  
  Purchase #7 $171.90   8.242%   $186.068   $186.07   $186.05   $186.10  
  7 purchase totals = $795.06       $849.0275   $849.04   $849.00   $849.10