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 $187.91   13.268%   $212.8419   $212.84   $212.85   $212.80  
  Purchase #2 $51.62   7.323%   $55.4001   $55.40   $55.40   $55.40  
  Purchase #3 $157.76   6.679%   $168.2968   $168.30   $168.30   $168.30  
  Purchase #4 $181.63   3.412%   $187.8272   $187.83   $187.85   $187.80  
  Purchase #5 $230.35   8.653%   $250.2822   $250.28   $250.30   $250.30  
  Purchase #6 $113.29   8.521%   $122.9434   $122.94   $122.95   $122.90  
  Purchase #7 $53.42   8.367%   $57.8897   $57.89   $57.90   $57.90  
  7 purchase totals = $975.98       $1,055.4813   $1,055.48   $1,055.55   $1,055.40