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 $237.69   12.223%   $266.7428   $266.74   $266.75   $266.70  
  Purchase #2 $44.59   3.360%   $46.0882   $46.09   $46.10   $46.10  
  Purchase #3 $60.28   3.405%   $62.3325   $62.33   $62.35   $62.30  
  Purchase #4 $118.51   4.308%   $123.6154   $123.62   $123.60   $123.60  
  Purchase #5 $46.95   5.152%   $49.3689   $49.37   $49.35   $49.40  
  Purchase #6 $214.41   12.513%   $241.2391   $241.24   $241.25   $241.20  
  Purchase #7 $49.49   9.478%   $54.1807   $54.18   $54.20   $54.20  
  7 purchase totals = $771.92       $843.5676   $843.57   $843.60   $843.50