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 $158.95   8.867%   $173.0441   $173.04   $173.05   $173.00  
  Purchase #2 $139.38   3.774%   $144.6402   $144.64   $144.65   $144.60  
  Purchase #3 $100.59   9.416%   $110.0616   $110.06   $110.05   $110.10  
  Purchase #4 $195.87   5.858%   $207.3441   $207.34   $207.35   $207.30  
  Purchase #5 $216.71   13.179%   $245.2702   $245.27   $245.25   $245.30  
  Purchase #6 $68.98   9.535%   $75.5572   $75.56   $75.55   $75.60  
  Purchase #7 $138.37   10.434%   $152.8075   $152.81   $152.80   $152.80  
  7 purchase totals = $1,018.85       $1,108.7249   $1,108.72   $1,108.70   $1,108.70