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 $56.56   9.514%   $61.9411   $61.94   $61.95   $61.90  
  Purchase #2 $18.62   10.733%   $20.6185   $20.62   $20.60   $20.60  
  Purchase #3 $202.74   5.640%   $214.1745   $214.17   $214.15   $214.20  
  Purchase #4 $196.97   8.308%   $213.3343   $213.33   $213.35   $213.30  
  Purchase #5 $149.42   10.424%   $164.9955   $165.00   $165.00   $165.00  
  Purchase #6 $200.39   6.361%   $213.1368   $213.14   $213.15   $213.10  
  Purchase #7 $157.64   13.453%   $178.8473   $178.85   $178.85   $178.80  
  7 purchase totals = $982.34       $1,067.0480   $1,067.05   $1,067.05   $1,066.90