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 $76.69   12.563%   $86.3246   $86.32   $86.30   $86.30  
  Purchase #2 $164.47   4.543%   $171.9419   $171.94   $171.95   $171.90  
  Purchase #3 $49.99   4.185%   $52.0821   $52.08   $52.10   $52.10  
  Purchase #4 $15.91   11.109%   $17.6774   $17.68   $17.70   $17.70  
  Purchase #5 $102.35   9.409%   $111.9801   $111.98   $112.00   $112.00  
  Purchase #6 $207.86   13.804%   $236.553   $236.55   $236.55   $236.60  
  Purchase #7 $189.74   11.682%   $211.9054   $211.91   $211.90   $211.90  
  7 purchase totals = $807.01       $888.4645   $888.46   $888.50   $888.50