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 $154.62   5.552%   $163.2045   $163.20   $163.20   $163.20  
  Purchase #2 $247.76   11.145%   $275.3729   $275.37   $275.35   $275.40  
  Purchase #3 $131.55   5.714%   $139.0668   $139.07   $139.05   $139.10  
  Purchase #4 $159.43   8.203%   $172.508   $172.51   $172.50   $172.50  
  Purchase #5 $176.54   3.283%   $182.3358   $182.34   $182.35   $182.30  
  Purchase #6 $33.85   11.804%   $37.8457   $37.85   $37.85   $37.80  
  Purchase #7 $226.65   3.670%   $234.9681   $234.97   $234.95   $235.00  
  7 purchase totals = $1,130.40       $1,205.3018   $1,205.31   $1,205.25   $1,205.30