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 $85.54   12.660%   $96.3694   $96.37   $96.35   $96.40  
  Purchase #2 $222.89   8.358%   $241.5191   $241.52   $241.50   $241.50  
  Purchase #3 $19.43   12.598%   $21.8778   $21.88   $21.90   $21.90  
  Purchase #4 $33.91   13.576%   $38.5136   $38.51   $38.50   $38.50  
  Purchase #5 $32.75   8.873%   $35.6559   $35.66   $35.65   $35.70  
  Purchase #6 $241.71   4.441%   $252.4443   $252.44   $252.45   $252.40  
  Purchase #7 $202.65   5.217%   $213.2223   $213.22   $213.20   $213.20  
  7 purchase totals = $838.88       $899.6024   $899.60   $899.55   $899.60