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 $209.56   11.658%   $233.9905   $233.99   $234.00   $234.00  
  Purchase #2 $58.94   11.207%   $65.5454   $65.55   $65.55   $65.50  
  Purchase #3 $163.94   11.736%   $183.18   $183.18   $183.20   $183.20  
  Purchase #4 $157.91   3.841%   $163.9753   $163.98   $164.00   $164.00  
  Purchase #5 $25.60   6.785%   $27.337   $27.34   $27.35   $27.30  
  Purchase #6 $128.77   13.539%   $146.2042   $146.20   $146.20   $146.20  
  Purchase #7 $163.78   9.192%   $178.8347   $178.83   $178.85   $178.80  
  7 purchase totals = $908.50       $999.0671   $999.07   $999.15   $999.00