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 $181.26   8.827%   $197.2598   $197.26   $197.25   $197.30  
  Purchase #2 $99.25   7.571%   $106.7642   $106.76   $106.75   $106.80  
  Purchase #3 $186.37   3.324%   $192.5649   $192.56   $192.55   $192.60  
  Purchase #4 $241.88   6.399%   $257.3579   $257.36   $257.35   $257.40  
  Purchase #5 $71.27   11.357%   $79.3641   $79.36   $79.35   $79.40  
  Purchase #6 $98.29   13.809%   $111.8629   $111.86   $111.85   $111.90  
  Purchase #7 $22.66   7.580%   $24.3776   $24.38   $24.40   $24.40  
  7 purchase totals = $900.98       $969.5514   $969.54   $969.50   $969.80