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 $241.28   11.322%   $268.5977   $268.60   $268.60   $268.60  
  Purchase #2 $224.81   11.841%   $251.4298   $251.43   $251.45   $251.40  
  Purchase #3 $34.28   8.129%   $37.0666   $37.07   $37.05   $37.10  
  Purchase #4 $14.92   8.121%   $16.1317   $16.13   $16.15   $16.10  
  Purchase #5 $94.35   10.753%   $104.4955   $104.50   $104.50   $104.50  
  Purchase #6 $143.75   5.214%   $151.2451   $151.25   $151.25   $151.20  
  Purchase #7 $131.33   5.126%   $138.062   $138.06   $138.05   $138.10  
  7 purchase totals = $884.72       $967.0284   $967.04   $967.05   $967.00