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 $59.34   11.267%   $66.0258   $66.03   $66.05   $66.00  
  Purchase #2 $32.50   3.327%   $33.5813   $33.58   $33.60   $33.60  
  Purchase #3 $63.49   3.828%   $65.9204   $65.92   $65.90   $65.90  
  Purchase #4 $45.80   13.458%   $51.9638   $51.96   $51.95   $52.00  
  Purchase #5 $184.90   9.706%   $202.8464   $202.85   $202.85   $202.80  
  Purchase #6 $79.61   8.406%   $86.302   $86.30   $86.30   $86.30  
  Purchase #7 $207.59   7.274%   $222.6901   $222.69   $222.70   $222.70  
  7 purchase totals = $673.23       $729.3298   $729.33   $729.35   $729.30