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 $82.96   12.439%   $93.2794   $93.28   $93.30   $93.30  
  Purchase #2 $60.58   10.302%   $66.821   $66.82   $66.80   $66.80  
  Purchase #3 $216.97   10.300%   $239.3179   $239.32   $239.30   $239.30  
  Purchase #4 $156.36   4.405%   $163.2477   $163.25   $163.25   $163.20  
  Purchase #5 $193.74   7.872%   $208.9912   $208.99   $209.00   $209.00  
  Purchase #6 $105.82   3.245%   $109.2539   $109.25   $109.25   $109.30  
  Purchase #7 $181.39   3.108%   $187.0276   $187.03   $187.05   $187.00  
  7 purchase totals = $997.82       $1,067.9387   $1,067.94   $1,067.95   $1,067.90