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 $77.92   11.134%   $86.5956   $86.60   $86.60   $86.60  
  Purchase #2 $120.77   9.454%   $132.1876   $132.19   $132.20   $132.20  
  Purchase #3 $210.49   5.613%   $222.3048   $222.30   $222.30   $222.30  
  Purchase #4 $105.52   9.552%   $115.5993   $115.60   $115.60   $115.60  
  Purchase #5 $63.66   5.293%   $67.0295   $67.03   $67.05   $67.00  
  Purchase #6 $209.52   5.849%   $221.7748   $221.77   $221.75   $221.80  
  Purchase #7 $232.40   11.478%   $259.0749   $259.07   $259.05   $259.10  
  7 purchase totals = $1,020.28       $1,104.5665   $1,104.56   $1,104.55   $1,104.60