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 $249.91   10.616%   $276.4404   $276.44   $276.45   $276.40  
  Purchase #2 $21.33   12.558%   $24.0086   $24.01   $24.00   $24.00  
  Purchase #3 $196.98   8.428%   $213.5815   $213.58   $213.60   $213.60  
  Purchase #4 $23.34   8.673%   $25.3643   $25.36   $25.35   $25.40  
  Purchase #5 $49.52   4.388%   $51.6929   $51.69   $51.70   $51.70  
  Purchase #6 $132.38   7.483%   $142.286   $142.29   $142.30   $142.30  
  Purchase #7 $216.75   7.457%   $232.913   $232.91   $232.90   $232.90  
  7 purchase totals = $890.21       $966.2867   $966.28   $966.30   $966.30