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 $141.29   12.473%   $158.9131   $158.91   $158.90   $158.90  
  Purchase #2 $85.89   8.329%   $93.0438   $93.04   $93.05   $93.00  
  Purchase #3 $21.75   12.424%   $24.4522   $24.45   $24.45   $24.50  
  Purchase #4 $244.78   12.635%   $275.708   $275.71   $275.70   $275.70  
  Purchase #5 $77.88   11.874%   $87.1275   $87.13   $87.15   $87.10  
  Purchase #6 $239.36   4.316%   $249.6908   $249.69   $249.70   $249.70  
  Purchase #7 $185.40   13.577%   $210.5718   $210.57   $210.55   $210.60  
  7 purchase totals = $996.35       $1,099.5072   $1,099.50   $1,099.50   $1,099.50