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 $56.44   9.831%   $61.9886   $61.99   $62.00   $62.00  
  Purchase #2 $223.74   10.371%   $246.9441   $246.94   $246.95   $246.90  
  Purchase #3 $119.34   13.324%   $135.2409   $135.24   $135.25   $135.20  
  Purchase #4 $248.69   9.351%   $271.945   $271.95   $271.95   $271.90  
  Purchase #5 $85.98   7.668%   $92.5729   $92.57   $92.55   $92.60  
  Purchase #6 $33.65   13.858%   $38.3132   $38.31   $38.30   $38.30  
  Purchase #7 $187.82   11.583%   $209.5752   $209.58   $209.60   $209.60  
  7 purchase totals = $955.66       $1,056.5799   $1,056.58   $1,056.60   $1,056.50