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	$73.35	8.359%	$79.4813	$79.48	$79.50	$79.50
Purchase #2	$53.38	3.473%	$55.2339	$55.23	$55.25	$55.20
Purchase #3	$232.58	4.844%	$243.8462	$243.85	$243.85	$243.80
Purchase #4	$215.38	5.145%	$226.4613	$226.46	$226.45	$226.50
Purchase #5	$239.70	10.439%	$264.7223	$264.72	$264.70	$264.70
Purchase #6	$112.32	13.642%	$127.6427	$127.64	$127.65	$127.60
Purchase #7	$128.40	13.328%	$145.5132	$145.51	$145.50	$145.50
7 purchase totals =	$1,055.11		$1,142.9009	$1,142.89	$1,142.90	$1,142.80