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 $86.93   6.807%   $92.8473   $92.85   $92.85   $92.80  
  Purchase #2 $45.39   4.800%   $47.5687   $47.57   $47.55   $47.60  
  Purchase #3 $55.28   10.155%   $60.8937   $60.89   $60.90   $60.90  
  Purchase #4 $179.66   4.481%   $187.7106   $187.71   $187.70   $187.70  
  Purchase #5 $226.68   3.659%   $234.9742   $234.97   $234.95   $235.00  
  Purchase #6 $191.91   8.466%   $208.1571   $208.16   $208.15   $208.20  
  Purchase #7 $166.28   4.107%   $173.1091   $173.11   $173.10   $173.10  
  7 purchase totals = $952.13       $1,005.2607   $1,005.26   $1,005.20   $1,005.30