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 $77.29   11.627%   $86.2765   $86.28   $86.30   $86.30  
  Purchase #2 $246.70   9.289%   $269.616   $269.62   $269.60   $269.60  
  Purchase #3 $188.83   9.248%   $206.293   $206.29   $206.30   $206.30  
  Purchase #4 $23.67   8.229%   $25.6178   $25.62   $25.60   $25.60  
  Purchase #5 $22.26   12.549%   $25.0534   $25.05   $25.05   $25.10  
  Purchase #6 $200.25   3.409%   $207.0765   $207.08   $207.10   $207.10  
  Purchase #7 $223.78   9.568%   $245.1913   $245.19   $245.20   $245.20  
  7 purchase totals = $982.78       $1,065.1245   $1,065.13   $1,065.15   $1,065.20