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 $61.80   6.215%   $65.6409   $65.64   $65.65   $65.60  
  Purchase #2 $175.73   9.405%   $192.2574   $192.26   $192.25   $192.30  
  Purchase #3 $17.33   3.508%   $17.9379   $17.94   $17.95   $17.90  
  Purchase #4 $250.97   3.207%   $259.0186   $259.02   $259.00   $259.00  
  Purchase #5 $166.84   5.469%   $175.9645   $175.96   $175.95   $176.00  
  Purchase #6 $171.44   11.642%   $191.399   $191.40   $191.40   $191.40  
  Purchase #7 $101.54   11.626%   $113.345   $113.35   $113.35   $113.30  
  7 purchase totals = $945.65       $1,015.5633   $1,015.57   $1,015.55   $1,015.50