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 $146.73   8.745%   $159.5615   $159.56   $159.55   $159.60  
  Purchase #2 $125.45   12.245%   $140.8114   $140.81   $140.80   $140.80  
  Purchase #3 $118.72   5.737%   $125.531   $125.53   $125.55   $125.50  
  Purchase #4 $173.49   6.824%   $185.329   $185.33   $185.35   $185.30  
  Purchase #5 $60.87   11.616%   $67.9407   $67.94   $67.95   $67.90  
  Purchase #6 $170.39   11.469%   $189.932   $189.93   $189.95   $189.90  
  Purchase #7 $164.76   12.710%   $185.701   $185.70   $185.70   $185.70  
  7 purchase totals = $960.41       $1,054.8066   $1,054.80   $1,054.85   $1,054.70