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 $86.69   8.276%   $93.8645   $93.86   $93.85   $93.90  
  Purchase #2 $248.95   11.248%   $276.9519   $276.95   $276.95   $277.00  
  Purchase #3 $84.35   12.450%   $94.8516   $94.85   $94.85   $94.90  
  Purchase #4 $246.33   10.596%   $272.4311   $272.43   $272.45   $272.40  
  Purchase #5 $98.92   9.683%   $108.4984   $108.50   $108.50   $108.50  
  Purchase #6 $170.92   8.265%   $185.0465   $185.05   $185.05   $185.00  
  Purchase #7 $117.42   8.652%   $127.5792   $127.58   $127.60   $127.60  
  7 purchase totals = $1,053.58       $1,159.2232   $1,159.22   $1,159.25   $1,159.30