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 $207.73   13.136%   $235.0174   $235.02   $235.00   $235.00  
  Purchase #2 $65.37   3.533%   $67.6795   $67.68   $67.70   $67.70  
  Purchase #3 $184.58   13.498%   $209.4946   $209.49   $209.50   $209.50  
  Purchase #4 $127.73   8.246%   $138.2626   $138.26   $138.25   $138.30  
  Purchase #5 $85.99   8.764%   $93.5262   $93.53   $93.55   $93.50  
  Purchase #6 $118.47   4.563%   $123.8758   $123.88   $123.90   $123.90  
  Purchase #7 $121.36   9.687%   $133.1161   $133.12   $133.10   $133.10  
  7 purchase totals = $911.23       $1,000.9722   $1,000.98   $1,001.00   $1,001.00