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 $70.65   8.232%   $76.4659   $76.47   $76.45   $76.50  
  Purchase #2 $103.29   3.212%   $106.6077   $106.61   $106.60   $106.60  
  Purchase #3 $98.40   4.172%   $102.5052   $102.51   $102.50   $102.50  
  Purchase #4 $87.45   5.660%   $92.3997   $92.40   $92.40   $92.40  
  Purchase #5 $46.80   6.775%   $49.9707   $49.97   $49.95   $50.00  
  Purchase #6 $230.26   7.804%   $248.2295   $248.23   $248.25   $248.20  
  Purchase #7 $106.34   4.590%   $111.221   $111.22   $111.20   $111.20  
  7 purchase totals = $743.19       $787.3997   $787.41   $787.35   $787.40