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 $59.73   10.398%   $65.9407   $65.94   $65.95   $65.90  
  Purchase #2 $31.64   8.671%   $34.3835   $34.38   $34.40   $34.40  
  Purchase #3 $236.80   5.506%   $249.8382   $249.84   $249.85   $249.80  
  Purchase #4 $70.46   5.565%   $74.3811   $74.38   $74.40   $74.40  
  Purchase #5 $153.46   9.165%   $167.5246   $167.52   $167.50   $167.50  
  Purchase #6 $116.72   11.451%   $130.0856   $130.09   $130.10   $130.10  
  Purchase #7 $165.62   6.813%   $176.9037   $176.90   $176.90   $176.90  
  7 purchase totals = $834.43       $899.0574   $899.05   $899.10   $899.00