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 $28.71   11.653%   $32.0556   $32.06   $32.05   $32.10  
  Purchase #2 $157.55   5.668%   $166.4799   $166.48   $166.50   $166.50  
  Purchase #3 $32.55   12.422%   $36.5934   $36.59   $36.60   $36.60  
  Purchase #4 $211.66   9.359%   $231.4693   $231.47   $231.45   $231.50  
  Purchase #5 $184.83   13.604%   $209.9743   $209.97   $209.95   $210.00  
  Purchase #6 $36.97   3.596%   $38.2994   $38.30   $38.30   $38.30  
  Purchase #7 $79.59   8.273%   $86.1745   $86.17   $86.15   $86.20  
  7 purchase totals = $731.86       $801.0464   $801.04   $801.00   $801.20