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 $176.69   4.522%   $184.6799   $184.68   $184.70   $184.70  
  Purchase #2 $209.77   5.574%   $221.4626   $221.46   $221.45   $221.50  
  Purchase #3 $103.55   5.626%   $109.3757   $109.38   $109.40   $109.40  
  Purchase #4 $224.94   3.266%   $232.2865   $232.29   $232.30   $232.30  
  Purchase #5 $106.75   4.726%   $111.795   $111.80   $111.80   $111.80  
  Purchase #6 $205.39   5.338%   $216.3537   $216.35   $216.35   $216.40  
  Purchase #7 $99.85   6.523%   $106.3632   $106.36   $106.35   $106.40  
  7 purchase totals = $1,126.94       $1,182.3166   $1,182.32   $1,182.35   $1,182.50