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 $7.55   4.121%   $7.8611   $7.86   $7.85   $7.90  
  Purchase #2 $164.41   4.146%   $171.2264   $171.23   $171.25   $171.20  
  Purchase #3 $12.55   7.379%   $13.4761   $13.48   $13.50   $13.50  
  Purchase #4 $163.44   11.272%   $181.863   $181.86   $181.85   $181.90  
  Purchase #5 $106.38   8.582%   $115.5095   $115.51   $115.50   $115.50  
  Purchase #6 $9.96   11.211%   $11.0766   $11.08   $11.10   $11.10  
  Purchase #7 $78.89   10.348%   $87.0535   $87.05   $87.05   $87.10  
  7 purchase totals = $543.18       $588.0662   $588.07   $588.10   $588.20