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 $245.95   11.247%   $273.612   $273.61   $273.60   $273.60  
  Purchase #2 $195.42   10.286%   $215.5209   $215.52   $215.50   $215.50  
  Purchase #3 $68.70   5.801%   $72.6853   $72.69   $72.70   $72.70  
  Purchase #4 $194.85   3.789%   $202.2329   $202.23   $202.25   $202.20  
  Purchase #5 $50.85   4.346%   $53.0599   $53.06   $53.05   $53.10  
  Purchase #6 $138.63   8.866%   $150.9209   $150.92   $150.90   $150.90  
  Purchase #7 $30.44   5.164%   $32.0119   $32.01   $32.00   $32.00  
  7 purchase totals = $924.84       $1,000.0438   $1,000.04   $1,000.00   $1,000.00