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 $242.26   10.726%   $268.2448   $268.24   $268.25   $268.20  
  Purchase #2 $227.32   12.144%   $254.9257   $254.93   $254.95   $254.90  
  Purchase #3 $27.73   6.530%   $29.5408   $29.54   $29.55   $29.50  
  Purchase #4 $201.75   12.778%   $227.5296   $227.53   $227.55   $227.50  
  Purchase #5 $20.47   5.387%   $21.5727   $21.57   $21.55   $21.60  
  Purchase #6 $31.98   8.608%   $34.7328   $34.73   $34.75   $34.70  
  Purchase #7 $203.67   3.616%   $211.0347   $211.03   $211.05   $211.00  
  7 purchase totals = $955.18       $1,047.5811   $1,047.57   $1,047.65   $1,047.40