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 $240.42   8.547%   $260.9687   $260.97   $260.95   $261.00  
  Purchase #2 $120.25   8.646%   $130.6468   $130.65   $130.65   $130.60  
  Purchase #3 $205.61   8.448%   $222.9799   $222.98   $223.00   $223.00  
  Purchase #4 $8.70   7.148%   $9.3219   $9.32   $9.30   $9.30  
  Purchase #5 $137.32   8.796%   $149.3987   $149.40   $149.40   $149.40  
  Purchase #6 $229.27   10.525%   $253.4007   $253.40   $253.40   $253.40  
  Purchase #7 $84.60   5.162%   $88.9671   $88.97   $88.95   $89.00  
  7 purchase totals = $1,026.17       $1,115.6838   $1,115.69   $1,115.65   $1,115.70