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 $85.55   12.109%   $95.9092   $95.91   $95.90   $95.90  
  Purchase #2 $146.34   3.614%   $151.6287   $151.63   $151.65   $151.60  
  Purchase #3 $191.93   11.395%   $213.8004   $213.80   $213.80   $213.80  
  Purchase #4 $11.29   12.754%   $12.7299   $12.73   $12.75   $12.70  
  Purchase #5 $79.34   7.279%   $85.1152   $85.12   $85.10   $85.10  
  Purchase #6 $191.29   10.113%   $210.6352   $210.64   $210.65   $210.60  
  Purchase #7 $81.58   13.789%   $92.8291   $92.83   $92.85   $92.80  
  7 purchase totals = $787.32       $862.6477   $862.66   $862.70   $862.50