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 $250.50   7.664%   $269.6983   $269.70   $269.70   $269.70  
  Purchase #2 $71.98   6.744%   $76.8343   $76.83   $76.85   $76.80  
  Purchase #3 $7.84   7.197%   $8.4042   $8.40   $8.40   $8.40  
  Purchase #4 $199.93   6.842%   $213.6092   $213.61   $213.60   $213.60  
  Purchase #5 $203.55   10.534%   $224.992   $224.99   $225.00   $225.00  
  Purchase #6 $216.61   10.233%   $238.7757   $238.78   $238.80   $238.80  
  Purchase #7 $26.70   11.205%   $29.6917   $29.69   $29.70   $29.70  
  7 purchase totals = $977.11       $1,062.0054   $1,062.00   $1,062.05   $1,062.00