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 $26.68   10.707%   $29.5366   $29.54   $29.55   $29.50  
  Purchase #2 $166.54   5.797%   $176.1943   $176.19   $176.20   $176.20  
  Purchase #3 $94.66   12.735%   $106.715   $106.72   $106.70   $106.70  
  Purchase #4 $95.45   5.401%   $100.6053   $100.61   $100.60   $100.60  
  Purchase #5 $48.25   6.545%   $51.408   $51.41   $51.40   $51.40  
  Purchase #6 $175.87   10.365%   $194.0989   $194.10   $194.10   $194.10  
  Purchase #7 $168.36   9.294%   $184.0074   $184.01   $184.00   $184.00  
  7 purchase totals = $775.81       $842.5655   $842.58   $842.55   $842.50