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 $61.80   11.687%   $69.0226   $69.02   $69.00   $69.00  
  Purchase #2 $102.65   10.794%   $113.73   $113.73   $113.75   $113.70  
  Purchase #3 $230.54   7.423%   $247.653   $247.65   $247.65   $247.70  
  Purchase #4 $174.46   6.773%   $186.2762   $186.28   $186.30   $186.30  
  Purchase #5 $103.75   7.814%   $111.857   $111.86   $111.85   $111.90  
  Purchase #6 $242.75   7.117%   $260.0265   $260.03   $260.05   $260.00  
  Purchase #7 $21.73   12.590%   $24.4658   $24.47   $24.45   $24.50  
  7 purchase totals = $937.68       $1,013.0311   $1,013.04   $1,013.05   $1,013.10