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 $187.54   8.659%   $203.7791   $203.78   $203.80   $203.80  
  Purchase #2 $47.97   10.333%   $52.9267   $52.93   $52.95   $52.90  
  Purchase #3 $101.91   8.808%   $110.8862   $110.89   $110.90   $110.90  
  Purchase #4 $114.63   8.505%   $124.3793   $124.38   $124.40   $124.40  
  Purchase #5 $165.64   12.106%   $185.6924   $185.69   $185.70   $185.70  
  Purchase #6 $230.77   6.384%   $245.5024   $245.50   $245.50   $245.50  
  Purchase #7 $69.25   11.842%   $77.4506   $77.45   $77.45   $77.50  
  7 purchase totals = $917.71       $1,000.6167   $1,000.62   $1,000.70   $1,000.70