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 $79.86   8.185%   $86.3965   $86.40   $86.40   $86.40  
  Purchase #2 $129.78   13.232%   $146.9525   $146.95   $146.95   $147.00  
  Purchase #3 $245.77   5.403%   $259.049   $259.05   $259.05   $259.00  
  Purchase #4 $157.64   10.186%   $173.6972   $173.70   $173.70   $173.70  
  Purchase #5 $244.91   3.124%   $252.561   $252.56   $252.55   $252.60  
  Purchase #6 $151.45   9.278%   $165.5015   $165.50   $165.50   $165.50  
  Purchase #7 $168.37   9.187%   $183.8382   $183.84   $183.85   $183.80  
  7 purchase totals = $1,177.78       $1,267.9959   $1,268.00   $1,268.00   $1,268.00