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	$166.63	4.738%	$174.5249	$174.52	$174.50	$174.50
Purchase #2	$150.57	6.333%	$160.1056	$160.11	$160.10	$160.10
Purchase #3	$250.77	13.865%	$285.5393	$285.54	$285.55	$285.50
Purchase #4	$54.85	3.240%	$56.6271	$56.63	$56.65	$56.60
Purchase #5	$55.33	3.322%	$57.1681	$57.17	$57.15	$57.20
Purchase #6	$96.47	6.862%	$103.0898	$103.09	$103.10	$103.10
Purchase #7	$246.48	3.341%	$254.7149	$254.71	$254.70	$254.70
7 purchase totals =	$1,021.10		$1,091.7697	$1,091.77	$1,091.75	$1,091.70