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 $195.36   8.829%   $212.6083   $212.61   $212.60   $212.60  
  Purchase #2 $12.93   12.392%   $14.5323   $14.53   $14.55   $14.50  
  Purchase #3 $126.45   13.419%   $143.4183   $143.42   $143.40   $143.40  
  Purchase #4 $39.85   13.198%   $45.1094   $45.11   $45.10   $45.10  
  Purchase #5 $124.39   9.258%   $135.906   $135.91   $135.90   $135.90  
  Purchase #6 $96.40   11.510%   $107.4956   $107.50   $107.50   $107.50  
  Purchase #7 $148.32   13.383%   $168.1697   $168.17   $168.15   $168.20  
  7 purchase totals = $743.70       $827.2396   $827.25   $827.20   $827.20