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 $206.77   8.159%   $223.6404   $223.64   $223.65   $223.60  
  Purchase #2 $160.97   12.745%   $181.4856   $181.49   $181.50   $181.50  
  Purchase #3 $33.39   4.366%   $34.8478   $34.85   $34.85   $34.80  
  Purchase #4 $58.79   11.854%   $65.759   $65.76   $65.75   $65.80  
  Purchase #5 $20.55   5.320%   $21.6433   $21.64   $21.65   $21.60  
  Purchase #6 $40.50   7.157%   $43.3986   $43.40   $43.40   $43.40  
  Purchase #7 $239.81   9.404%   $262.3617   $262.36   $262.35   $262.40  
  7 purchase totals = $760.78       $833.1364   $833.14   $833.15   $833.10