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 $20.60   4.730%   $21.5744   $21.57   $21.55   $21.60  
  Purchase #2 $62.68   7.628%   $67.4612   $67.46   $67.45   $67.50  
  Purchase #3 $143.80   7.160%   $154.0961   $154.10   $154.10   $154.10  
  Purchase #4 $13.58   3.345%   $14.0343   $14.03   $14.05   $14.00  
  Purchase #5 $31.83   9.774%   $34.9411   $34.94   $34.95   $34.90  
  Purchase #6 $180.72   4.173%   $188.2614   $188.26   $188.25   $188.30  
  Purchase #7 $76.65   8.326%   $83.0319   $83.03   $83.05   $83.00  
  7 purchase totals = $529.86       $563.4004   $563.39   $563.40   $563.40