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 $92.73   4.627%   $97.0206   $97.02   $97.00   $97.00  
  Purchase #2 $178.49   11.522%   $199.0556   $199.06   $199.05   $199.10  
  Purchase #3 $106.35   13.565%   $120.7764   $120.78   $120.80   $120.80  
  Purchase #4 $102.67   3.152%   $105.9062   $105.91   $105.90   $105.90  
  Purchase #5 $196.30   9.203%   $214.3655   $214.37   $214.35   $214.40  
  Purchase #6 $80.60   6.659%   $85.9672   $85.97   $85.95   $86.00  
  Purchase #7 $233.99   4.279%   $244.0024   $244.00   $244.00   $244.00  
  7 purchase totals = $991.13       $1,067.0939   $1,067.11   $1,067.05   $1,067.20