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 $59.94   8.864%   $65.2531   $65.25   $65.25   $65.30  
  Purchase #2 $249.90   10.843%   $276.9967   $277.00   $277.00   $277.00  
  Purchase #3 $113.61   4.169%   $118.3464   $118.35   $118.35   $118.30  
  Purchase #4 $15.84   13.682%   $18.0072   $18.01   $18.00   $18.00  
  Purchase #5 $208.78   5.450%   $220.1585   $220.16   $220.15   $220.20  
  Purchase #6 $112.51   5.194%   $118.3538   $118.35   $118.35   $118.40  
  Purchase #7 $73.93   9.452%   $80.9179   $80.92   $80.90   $80.90  
  7 purchase totals = $834.51       $898.0336   $898.04   $898.00   $898.10