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 $246.87   7.156%   $264.536   $264.54   $264.55   $264.50  
  Purchase #2 $109.79   11.451%   $122.3621   $122.36   $122.35   $122.40  
  Purchase #3 $164.38   7.454%   $176.6329   $176.63   $176.65   $176.60  
  Purchase #4 $228.25   5.462%   $240.717   $240.72   $240.70   $240.70  
  Purchase #5 $139.28   8.508%   $151.1299   $151.13   $151.15   $151.10  
  Purchase #6 $56.57   13.702%   $64.3212   $64.32   $64.30   $64.30  
  Purchase #7 $39.99   4.258%   $41.6928   $41.69   $41.70   $41.70  
  7 purchase totals = $985.13       $1,061.3919   $1,061.39   $1,061.40   $1,061.30