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 $154.33   6.631%   $164.5636   $164.56   $164.55   $164.60  
  Purchase #2 $49.34   7.420%   $53.001   $53.00   $53.00   $53.00  
  Purchase #3 $42.47   10.463%   $46.9136   $46.91   $46.90   $46.90  
  Purchase #4 $160.87   3.160%   $165.9535   $165.95   $165.95   $166.00  
  Purchase #5 $64.33   5.797%   $68.0592   $68.06   $68.05   $68.10  
  Purchase #6 $10.47   4.239%   $10.9138   $10.91   $10.90   $10.90  
  Purchase #7 $162.38   8.825%   $176.71   $176.71   $176.70   $176.70  
  7 purchase totals = $644.19       $686.1147   $686.10   $686.05   $686.20