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 $183.85   13.117%   $207.9656   $207.97   $207.95   $208.00  
  Purchase #2 $57.96   11.533%   $64.6445   $64.64   $64.65   $64.60  
  Purchase #3 $141.95   10.336%   $156.622   $156.62   $156.60   $156.60  
  Purchase #4 $162.39   6.559%   $173.0412   $173.04   $173.05   $173.00  
  Purchase #5 $112.30   5.711%   $118.7135   $118.71   $118.70   $118.70  
  Purchase #6 $118.74   10.138%   $130.7779   $130.78   $130.80   $130.80  
  Purchase #7 $11.58   11.417%   $12.9021   $12.90   $12.90   $12.90  
  7 purchase totals = $788.77       $864.6668   $864.66   $864.65   $864.60