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 $221.58   11.489%   $247.0373   $247.04   $247.05   $247.00  
  Purchase #2 $95.72   11.804%   $107.0188   $107.02   $107.00   $107.00  
  Purchase #3 $127.26   8.179%   $137.6686   $137.67   $137.65   $137.70  
  Purchase #4 $97.65   9.633%   $107.0566   $107.06   $107.05   $107.10  
  Purchase #5 $20.63   6.674%   $22.0068   $22.01   $22.00   $22.00  
  Purchase #6 $25.36   8.585%   $27.5372   $27.54   $27.55   $27.50  
  Purchase #7 $210.56   11.126%   $233.9869   $233.99   $234.00   $234.00  
  7 purchase totals = $798.76       $882.3122   $882.33   $882.30   $882.30