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	$56.95	13.186%	$64.4594	$64.46	$64.45	$64.50
Purchase #2	$249.36	7.830%	$268.8849	$268.88	$268.90	$268.90
Purchase #3	$202.89	10.727%	$224.654	$224.65	$224.65	$224.70
Purchase #4	$174.40	8.491%	$189.2083	$189.21	$189.20	$189.20
Purchase #5	$43.31	4.665%	$45.3304	$45.33	$45.35	$45.30
Purchase #6	$127.86	4.463%	$133.5664	$133.57	$133.55	$133.60
Purchase #7	$226.96	11.619%	$253.3305	$253.33	$253.35	$253.30
7 purchase totals =	$1,081.73		$1,179.4339	$1,179.43	$1,179.45	$1,179.50