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 $59.30   9.533%   $64.9531   $64.95   $64.95   $65.00  
  Purchase #2 $123.61   11.336%   $137.6224   $137.62   $137.60   $137.60  
  Purchase #3 $137.58   11.257%   $153.0674   $153.07   $153.05   $153.10  
  Purchase #4 $247.51   11.252%   $275.3598   $275.36   $275.35   $275.40  
  Purchase #5 $194.68   12.549%   $219.1104   $219.11   $219.10   $219.10  
  Purchase #6 $226.60   11.627%   $252.9468   $252.95   $252.95   $252.90  
  Purchase #7 $163.66   11.318%   $182.183   $182.18   $182.20   $182.20  
  7 purchase totals = $1,152.94       $1,285.2429   $1,285.24   $1,285.20   $1,285.30