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 $60.98   10.316%   $67.2707   $67.27   $67.25   $67.30  
  Purchase #2 $177.42   8.821%   $193.0702   $193.07   $193.05   $193.10  
  Purchase #3 $142.91   11.613%   $159.5061   $159.51   $159.50   $159.50  
  Purchase #4 $86.50   10.565%   $95.6387   $95.64   $95.65   $95.60  
  Purchase #5 $163.95   13.270%   $185.7062   $185.71   $185.70   $185.70  
  Purchase #6 $173.71   6.257%   $184.579   $184.58   $184.60   $184.60  
  Purchase #7 $80.67   8.159%   $87.2519   $87.25   $87.25   $87.30  
  7 purchase totals = $886.14       $973.0228   $973.03   $973.00   $973.10