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 $144.44   11.518%   $161.0766   $161.08   $161.10   $161.10  
  Purchase #2 $201.97   7.185%   $216.4815   $216.48   $216.50   $216.50  
  Purchase #3 $153.60   13.113%   $173.7416   $173.74   $173.75   $173.70  
  Purchase #4 $68.97   8.194%   $74.6214   $74.62   $74.60   $74.60  
  Purchase #5 $67.72   12.639%   $76.2791   $76.28   $76.30   $76.30  
  Purchase #6 $101.90   6.156%   $108.173   $108.17   $108.15   $108.20  
  Purchase #7 $226.36   8.477%   $245.5485   $245.55   $245.55   $245.50  
  7 purchase totals = $964.96       $1,055.9217   $1,055.92   $1,055.95   $1,055.90