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 $168.80   11.268%   $187.8204   $187.82   $187.80   $187.80  
  Purchase #2 $182.61   12.806%   $205.995   $206.00   $206.00   $206.00  
  Purchase #3 $200.28   13.417%   $227.1516   $227.15   $227.15   $227.20  
  Purchase #4 $64.57   8.259%   $69.9028   $69.90   $69.90   $69.90  
  Purchase #5 $113.74   3.268%   $117.457   $117.46   $117.45   $117.50  
  Purchase #6 $118.72   5.289%   $124.9991   $125.00   $125.00   $125.00  
  Purchase #7 $206.87   8.529%   $224.5139   $224.51   $224.50   $224.50  
  7 purchase totals = $1,055.59       $1,157.8398   $1,157.84   $1,157.80   $1,157.90