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 $156.33   8.440%   $169.5243   $169.52   $169.50   $169.50  
  Purchase #2 $236.36   7.538%   $254.1768   $254.18   $254.20   $254.20  
  Purchase #3 $46.66   5.305%   $49.1353   $49.14   $49.15   $49.10  
  Purchase #4 $93.75   5.479%   $98.8866   $98.89   $98.90   $98.90  
  Purchase #5 $194.31   9.596%   $212.956   $212.96   $212.95   $213.00  
  Purchase #6 $157.26   7.284%   $168.7148   $168.71   $168.70   $168.70  
  Purchase #7 $47.90   7.607%   $51.5438   $51.54   $51.55   $51.50  
  7 purchase totals = $932.57       $1,004.9376   $1,004.94   $1,004.95   $1,004.90