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 $71.49   10.853%   $79.2488   $79.25   $79.25   $79.20  
  Purchase #2 $244.71   8.760%   $266.1466   $266.15   $266.15   $266.10  
  Purchase #3 $208.98   8.246%   $226.2125   $226.21   $226.20   $226.20  
  Purchase #4 $213.87   11.620%   $238.7217   $238.72   $238.70   $238.70  
  Purchase #5 $66.83   10.732%   $74.0022   $74.00   $74.00   $74.00  
  Purchase #6 $23.74   10.732%   $26.2878   $26.29   $26.30   $26.30  
  Purchase #7 $138.77   12.812%   $156.5492   $156.55   $156.55   $156.50  
  7 purchase totals = $968.39       $1,067.1688   $1,067.17   $1,067.15   $1,067.00