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 $86.52   11.798%   $96.7276   $96.73   $96.75   $96.70  
  Purchase #2 $185.47   4.477%   $193.7735   $193.77   $193.75   $193.80  
  Purchase #3 $90.35   11.723%   $100.9417   $100.94   $100.95   $100.90  
  Purchase #4 $235.42   6.509%   $250.7435   $250.74   $250.75   $250.70  
  Purchase #5 $61.48   10.285%   $67.8032   $67.80   $67.80   $67.80  
  Purchase #6 $221.99   11.647%   $247.8452   $247.85   $247.85   $247.80  
  Purchase #7 $242.31   12.458%   $272.497   $272.50   $272.50   $272.50  
  7 purchase totals = $1,123.54       $1,230.3317   $1,230.33   $1,230.35   $1,230.20