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 $146.68   11.620%   $163.7242   $163.72   $163.70   $163.70  
  Purchase #2 $146.38   10.321%   $161.4879   $161.49   $161.50   $161.50  
  Purchase #3 $64.35   8.858%   $70.0501   $70.05   $70.05   $70.10  
  Purchase #4 $237.53   3.603%   $246.0882   $246.09   $246.10   $246.10  
  Purchase #5 $124.42   5.803%   $131.6401   $131.64   $131.65   $131.60  
  Purchase #6 $80.41   7.324%   $86.2992   $86.30   $86.30   $86.30  
  Purchase #7 $161.78   5.367%   $170.4627   $170.46   $170.45   $170.50  
  7 purchase totals = $961.55       $1,029.7524   $1,029.75   $1,029.75   $1,029.80