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	$52.91	3.591%	$54.81	$54.81	$54.80	$54.80
Purchase #2	$247.99	12.111%	$278.0241	$278.02	$278.00	$278.00
Purchase #3	$245.92	7.657%	$264.7501	$264.75	$264.75	$264.80
Purchase #4	$188.46	12.399%	$211.8272	$211.83	$211.85	$211.80
Purchase #5	$40.56	13.193%	$45.9111	$45.91	$45.90	$45.90
Purchase #6	$30.53	4.429%	$31.8822	$31.88	$31.90	$31.90
Purchase #7	$120.89	7.653%	$130.1417	$130.14	$130.15	$130.10
7 purchase totals =	$927.26		$1,017.3464	$1,017.34	$1,017.35	$1,017.30