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	$51.54	7.305%	$55.305	$55.31	$55.30	$55.30
Purchase #2	$156.39	9.654%	$171.4879	$171.49	$171.50	$171.50
Purchase #3	$127.33	5.419%	$134.23	$134.23	$134.25	$134.20
Purchase #4	$245.25	4.323%	$255.8522	$255.85	$255.85	$255.90
Purchase #5	$94.77	11.794%	$105.9472	$105.95	$105.95	$105.90
Purchase #6	$147.81	7.648%	$159.1145	$159.11	$159.10	$159.10
Purchase #7	$169.60	3.590%	$175.6886	$175.69	$175.70	$175.70
7 purchase totals =	$992.69		$1,057.6254	$1,057.63	$1,057.65	$1,057.60