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 $161.93   9.527%   $177.3571   $177.36   $177.35   $177.40  
  Purchase #2 $143.97   5.836%   $152.3721   $152.37   $152.35   $152.40  
  Purchase #3 $128.54   3.793%   $133.4155   $133.42   $133.40   $133.40  
  Purchase #4 $218.49   10.260%   $240.9071   $240.91   $240.90   $240.90  
  Purchase #5 $46.27   13.776%   $52.6442   $52.64   $52.65   $52.60  
  Purchase #6 $187.66   11.695%   $209.6068   $209.61   $209.60   $209.60  
  Purchase #7 $13.51   9.751%   $14.8274   $14.83   $14.85   $14.80  
  7 purchase totals = $900.37       $981.1302   $981.14   $981.10   $981.10