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 $224.76   7.694%   $242.053   $242.05   $242.05   $242.10  
  Purchase #2 $46.61   7.239%   $49.9841   $49.98   $50.00   $50.00  
  Purchase #3 $136.61   13.782%   $155.4376   $155.44   $155.45   $155.40  
  Purchase #4 $243.89   9.764%   $267.7034   $267.70   $267.70   $267.70  
  Purchase #5 $59.61   9.474%   $65.2575   $65.26   $65.25   $65.30  
  Purchase #6 $185.87   8.712%   $202.063   $202.06   $202.05   $202.10  
  Purchase #7 $162.91   12.333%   $183.0017   $183.00   $183.00   $183.00  
  7 purchase totals = $1,060.26       $1,165.5003   $1,165.49   $1,165.50   $1,165.60