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 $146.95   6.177%   $156.0271   $156.03   $156.05   $156.00  
  Purchase #2 $72.91   12.365%   $81.9253   $81.93   $81.95   $81.90  
  Purchase #3 $198.66   5.152%   $208.895   $208.90   $208.90   $208.90  
  Purchase #4 $103.48   11.454%   $115.3326   $115.33   $115.35   $115.30  
  Purchase #5 $177.48   4.171%   $184.8827   $184.88   $184.90   $184.90  
  Purchase #6 $200.73   4.357%   $209.4758   $209.48   $209.50   $209.50  
  Purchase #7 $86.51   8.140%   $93.5519   $93.55   $93.55   $93.60  
  7 purchase totals = $986.72       $1,050.0904   $1,050.10   $1,050.20   $1,050.10