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 $73.40   3.822%   $76.2053   $76.21   $76.20   $76.20  
  Purchase #2 $113.32   4.324%   $118.22   $118.22   $118.20   $118.20  
  Purchase #3 $176.55   13.610%   $200.5785   $200.58   $200.60   $200.60  
  Purchase #4 $25.27   5.536%   $26.6689   $26.67   $26.65   $26.70  
  Purchase #5 $88.65   8.250%   $95.9636   $95.96   $95.95   $96.00  
  Purchase #6 $127.89   7.787%   $137.8488   $137.85   $137.85   $137.80  
  Purchase #7 $132.73   6.367%   $141.1809   $141.18   $141.20   $141.20  
  7 purchase totals = $737.81       $796.6660   $796.67   $796.65   $796.70