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	$134.47	8.227%	$145.5328	$145.53	$145.55	$145.50
Purchase #2	$55.92	4.521%	$58.4481	$58.45	$58.45	$58.40
Purchase #3	$165.54	12.296%	$185.8948	$185.89	$185.90	$185.90
Purchase #4	$42.72	11.755%	$47.7417	$47.74	$47.75	$47.70
Purchase #5	$250.92	10.314%	$276.7999	$276.80	$276.80	$276.80
Purchase #6	$213.44	9.337%	$233.3689	$233.37	$233.35	$233.40
Purchase #7	$154.98	6.510%	$165.0692	$165.07	$165.05	$165.10
7 purchase totals =	$1,017.99		$1,112.8554	$1,112.85	$1,112.85	$1,112.80