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 $40.49   3.371%   $41.8549   $41.85   $41.85   $41.90  
  Purchase #2 $172.35   12.356%   $193.6456   $193.65   $193.65   $193.60  
  Purchase #3 $96.45   4.278%   $100.5761   $100.58   $100.60   $100.60  
  Purchase #4 $240.91   5.142%   $253.2976   $253.30   $253.30   $253.30  
  Purchase #5 $141.87   13.873%   $161.5516   $161.55   $161.55   $161.60  
  Purchase #6 $14.60   12.562%   $16.4341   $16.43   $16.45   $16.40  
  Purchase #7 $217.25   10.236%   $239.4877   $239.49   $239.50   $239.50  
  7 purchase totals = $923.92       $1,006.8476   $1,006.85   $1,006.90   $1,006.90