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	$129.76	9.683%	$142.3247	$142.32	$142.30	$142.30
Purchase #2	$40.41	13.299%	$45.7841	$45.78	$45.80	$45.80
Purchase #3	$195.42	10.453%	$215.8473	$215.85	$215.85	$215.80
Purchase #4	$188.59	13.250%	$213.5782	$213.58	$213.60	$213.60
Purchase #5	$175.92	13.767%	$200.1389	$200.14	$200.15	$200.10
Purchase #6	$238.95	4.587%	$249.9106	$249.91	$249.90	$249.90
Purchase #7	$71.59	7.702%	$77.1039	$77.10	$77.10	$77.10
7 purchase totals =	$1,040.64		$1,144.6877	$1,144.68	$1,144.70	$1,144.60