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 $242.98   4.374%   $253.6079   $253.61   $253.60   $253.60  
  Purchase #2 $61.27   12.383%   $68.8571   $68.86   $68.85   $68.90  
  Purchase #3 $210.93   11.490%   $235.1659   $235.17   $235.15   $235.20  
  Purchase #4 $151.27   6.670%   $161.3597   $161.36   $161.35   $161.40  
  Purchase #5 $206.64   11.295%   $229.98   $229.98   $230.00   $230.00  
  Purchase #6 $248.41   6.691%   $265.0311   $265.03   $265.05   $265.00  
  Purchase #7 $113.42   5.159%   $119.2713   $119.27   $119.25   $119.30  
  7 purchase totals = $1,234.92       $1,333.2730   $1,333.28   $1,333.25   $1,333.40