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 $38.25   13.490%   $43.4099   $43.41   $43.40   $43.40  
  Purchase #2 $102.99   12.397%   $115.7577   $115.76   $115.75   $115.80  
  Purchase #3 $212.88   6.607%   $226.945   $226.95   $226.95   $226.90  
  Purchase #4 $180.92   4.577%   $189.2007   $189.20   $189.20   $189.20  
  Purchase #5 $212.76   13.503%   $241.489   $241.49   $241.50   $241.50  
  Purchase #6 $233.87   7.840%   $252.2054   $252.21   $252.20   $252.20  
  Purchase #7 $241.32   3.833%   $250.5698   $250.57   $250.55   $250.60  
  7 purchase totals = $1,222.99       $1,319.5775   $1,319.59   $1,319.55   $1,319.60