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 $184.91   12.861%   $208.6913   $208.69   $208.70   $208.70  
  Purchase #2 $246.28   6.575%   $262.4729   $262.47   $262.45   $262.50  
  Purchase #3 $103.73   11.305%   $115.4567   $115.46   $115.45   $115.50  
  Purchase #4 $22.80   13.430%   $25.862   $25.86   $25.85   $25.90  
  Purchase #5 $18.91   6.700%   $20.177   $20.18   $20.20   $20.20  
  Purchase #6 $249.77   3.158%   $257.6577   $257.66   $257.65   $257.70  
  Purchase #7 $200.73   12.787%   $226.3973   $226.40   $226.40   $226.40  
  7 purchase totals = $1,027.13       $1,116.7149   $1,116.72   $1,116.70   $1,116.90