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 $86.74   6.716%   $92.5655   $92.57   $92.55   $92.60  
  Purchase #2 $147.90   12.452%   $166.3165   $166.32   $166.30   $166.30  
  Purchase #3 $108.62   7.732%   $117.0185   $117.02   $117.00   $117.00  
  Purchase #4 $118.39   11.503%   $132.0084   $132.01   $132.00   $132.00  
  Purchase #5 $230.55   12.258%   $258.8108   $258.81   $258.80   $258.80  
  Purchase #6 $44.45   7.614%   $47.8344   $47.83   $47.85   $47.80  
  Purchase #7 $187.81   11.634%   $209.6598   $209.66   $209.65   $209.70  
  7 purchase totals = $924.46       $1,024.2139   $1,024.22   $1,024.15   $1,024.20