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 $136.97   11.188%   $152.2942   $152.29   $152.30   $152.30  
  Purchase #2 $106.41   12.456%   $119.6644   $119.66   $119.65   $119.70  
  Purchase #3 $71.30   6.791%   $76.142   $76.14   $76.15   $76.10  
  Purchase #4 $19.56   4.497%   $20.4396   $20.44   $20.45   $20.40  
  Purchase #5 $205.80   10.610%   $227.6354   $227.64   $227.65   $227.60  
  Purchase #6 $180.80   9.663%   $198.2707   $198.27   $198.25   $198.30  
  Purchase #7 $124.49   10.489%   $137.5478   $137.55   $137.55   $137.50  
  7 purchase totals = $845.33       $931.9941   $931.99   $932.00   $931.90