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 $61.79   5.612%   $65.2577   $65.26   $65.25   $65.30  
  Purchase #2 $193.89   6.509%   $206.5103   $206.51   $206.50   $206.50  
  Purchase #3 $35.45   6.299%   $37.683   $37.68   $37.70   $37.70  
  Purchase #4 $250.84   13.317%   $284.2444   $284.24   $284.25   $284.20  
  Purchase #5 $180.33   8.136%   $195.0016   $195.00   $195.00   $195.00  
  Purchase #6 $151.96   9.280%   $166.0619   $166.06   $166.05   $166.10  
  Purchase #7 $150.51   9.850%   $165.3352   $165.34   $165.35   $165.30  
  7 purchase totals = $1,024.77       $1,120.0941   $1,120.09   $1,120.10   $1,120.10