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 $49.58   8.749%   $53.9178   $53.92   $53.90   $53.90  
  Purchase #2 $158.34   11.307%   $176.2435   $176.24   $176.25   $176.20  
  Purchase #3 $81.31   7.472%   $87.3855   $87.39   $87.40   $87.40  
  Purchase #4 $242.81   6.753%   $259.207   $259.21   $259.20   $259.20  
  Purchase #5 $78.86   8.654%   $85.6845   $85.68   $85.70   $85.70  
  Purchase #6 $98.94   4.390%   $103.2835   $103.28   $103.30   $103.30  
  Purchase #7 $209.86   12.218%   $235.5007   $235.50   $235.50   $235.50  
  7 purchase totals = $919.70       $1,001.2225   $1,001.22   $1,001.25   $1,001.20