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	$38.58	12.524%	$43.4118	$43.41	$43.40	$43.40
Purchase #2	$166.63	4.568%	$174.2417	$174.24	$174.25	$174.20
Purchase #3	$161.66	3.468%	$167.2664	$167.27	$167.25	$167.30
Purchase #4	$96.41	6.330%	$102.5128	$102.51	$102.50	$102.50
Purchase #5	$185.76	5.865%	$196.6548	$196.65	$196.65	$196.70
Purchase #6	$136.28	3.288%	$140.7609	$140.76	$140.75	$140.80
Purchase #7	$169.25	5.767%	$179.0106	$179.01	$179.00	$179.00
7 purchase totals =	$954.57		$1,003.8590	$1,003.85	$1,003.80	$1,003.90