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 $85.34   11.301%   $94.9843   $94.98   $95.00   $95.00  
  Purchase #2 $171.30   10.469%   $189.2334   $189.23   $189.25   $189.20  
  Purchase #3 $223.49   9.767%   $245.3183   $245.32   $245.30   $245.30  
  Purchase #4 $82.27   10.189%   $90.6525   $90.65   $90.65   $90.70  
  Purchase #5 $114.48   6.760%   $122.2188   $122.22   $122.20   $122.20  
  Purchase #6 $30.70   10.141%   $33.8133   $33.81   $33.80   $33.80  
  Purchase #7 $202.94   9.451%   $222.1199   $222.12   $222.10   $222.10  
  7 purchase totals = $910.52       $998.3405   $998.33   $998.30   $998.30