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	$140.88	8.303%	$152.5773	$152.58	$152.60	$152.60
Purchase #2	$80.45	7.474%	$86.4628	$86.46	$86.45	$86.50
Purchase #3	$67.56	6.245%	$71.7791	$71.78	$71.80	$71.80
Purchase #4	$210.39	13.437%	$238.6601	$238.66	$238.65	$238.70
Purchase #5	$102.54	8.358%	$111.1103	$111.11	$111.10	$111.10
Purchase #6	$127.53	7.136%	$136.6305	$136.63	$136.65	$136.60
Purchase #7	$97.74	6.682%	$104.271	$104.27	$104.25	$104.30
7 purchase totals =	$827.09		$901.4911	$901.49	$901.50	$901.60