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 $60.97   8.329%   $66.0482   $66.05   $66.05   $66.00  
  Purchase #2 $165.59   10.649%   $183.2237   $183.22   $183.20   $183.20  
  Purchase #3 $80.47   4.874%   $84.3921   $84.39   $84.40   $84.40  
  Purchase #4 $220.59   9.871%   $242.3644   $242.36   $242.35   $242.40  
  Purchase #5 $130.60   13.339%   $148.0207   $148.02   $148.00   $148.00  
  Purchase #6 $237.91   6.244%   $252.7651   $252.77   $252.75   $252.80  
  Purchase #7 $112.77   6.329%   $119.9072   $119.91   $119.90   $119.90  
  7 purchase totals = $1,008.90       $1,096.7214   $1,096.72   $1,096.65   $1,096.70