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 $184.60   12.381%   $207.4553   $207.46   $207.45   $207.50  
  Purchase #2 $114.74   9.772%   $125.9524   $125.95   $125.95   $126.00  
  Purchase #3 $115.59   11.349%   $128.7083   $128.71   $128.70   $128.70  
  Purchase #4 $51.50   13.334%   $58.367   $58.37   $58.35   $58.40  
  Purchase #5 $191.92   3.378%   $198.4031   $198.40   $198.40   $198.40  
  Purchase #6 $216.61   6.170%   $229.9748   $229.97   $229.95   $230.00  
  Purchase #7 $197.95   5.612%   $209.059   $209.06   $209.05   $209.10  
  7 purchase totals = $1,072.91       $1,157.9199   $1,157.92   $1,157.85   $1,158.10