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 $59.89   13.833%   $68.1746   $68.17   $68.15   $68.20  
  Purchase #2 $140.95   8.482%   $152.9054   $152.91   $152.90   $152.90  
  Purchase #3 $83.39   5.242%   $87.7613   $87.76   $87.75   $87.80  
  Purchase #4 $109.31   7.655%   $117.6777   $117.68   $117.70   $117.70  
  Purchase #5 $75.99   12.390%   $85.4052   $85.41   $85.40   $85.40  
  Purchase #6 $146.33   13.841%   $166.5835   $166.58   $166.60   $166.60  
  Purchase #7 $103.73   9.121%   $113.1912   $113.19   $113.20   $113.20  
  7 purchase totals = $719.59       $791.6989   $791.70   $791.70   $791.80