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 $62.94   3.261%   $64.9925   $64.99   $65.00   $65.00  
  Purchase #2 $6.33   4.618%   $6.6223   $6.62   $6.60   $6.60  
  Purchase #3 $144.66   4.309%   $150.8934   $150.89   $150.90   $150.90  
  Purchase #4 $223.28   13.126%   $252.5877   $252.59   $252.60   $252.60  
  Purchase #5 $234.88   10.178%   $258.7861   $258.79   $258.80   $258.80  
  Purchase #6 $55.43   3.492%   $57.3656   $57.37   $57.35   $57.40  
  Purchase #7 $242.82   13.660%   $275.9892   $275.99   $276.00   $276.00  
  7 purchase totals = $970.34       $1,067.2368   $1,067.24   $1,067.25   $1,067.30