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 $88.99   6.808%   $95.0484   $95.05   $95.05   $95.00  
  Purchase #2 $40.69   11.152%   $45.2277   $45.23   $45.25   $45.20  
  Purchase #3 $199.48   10.766%   $220.956   $220.96   $220.95   $221.00  
  Purchase #4 $165.38   8.239%   $179.0057   $179.01   $179.00   $179.00  
  Purchase #5 $148.78   7.794%   $160.3759   $160.38   $160.40   $160.40  
  Purchase #6 $249.48   13.458%   $283.055   $283.06   $283.05   $283.10  
  Purchase #7 $175.87   13.559%   $199.7162   $199.72   $199.70   $199.70  
  7 purchase totals = $1,068.67       $1,183.3849   $1,183.41   $1,183.40   $1,183.40