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 $85.45   8.744%   $92.9217   $92.92   $92.90   $92.90  
  Purchase #2 $228.70   8.701%   $248.5992   $248.60   $248.60   $248.60  
  Purchase #3 $171.74   6.366%   $182.673   $182.67   $182.65   $182.70  
  Purchase #4 $16.43   7.183%   $17.6102   $17.61   $17.60   $17.60  
  Purchase #5 $66.96   12.196%   $75.1264   $75.13   $75.15   $75.10  
  Purchase #6 $141.44   7.678%   $152.2998   $152.30   $152.30   $152.30  
  Purchase #7 $162.65   8.727%   $176.8445   $176.84   $176.85   $176.80  
  7 purchase totals = $873.37       $946.0748   $946.07   $946.05   $946.00