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 $68.50   10.631%   $75.7822   $75.78   $75.80   $75.80  
  Purchase #2 $25.44   3.444%   $26.3162   $26.32   $26.30   $26.30  
  Purchase #3 $204.49   8.409%   $221.6856   $221.69   $221.70   $221.70  
  Purchase #4 $228.84   12.556%   $257.5732   $257.57   $257.55   $257.60  
  Purchase #5 $200.80   10.604%   $222.0928   $222.09   $222.10   $222.10  
  Purchase #6 $106.95   4.106%   $111.3414   $111.34   $111.35   $111.30  
  Purchase #7 $232.48   6.106%   $246.6752   $246.68   $246.70   $246.70  
  7 purchase totals = $1,067.50       $1,161.4666   $1,161.47   $1,161.50   $1,161.50