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	$52.44	5.167%	$55.1496	$55.15	$55.15	$55.10
Purchase #2	$194.85	8.139%	$210.7088	$210.71	$210.70	$210.70
Purchase #3	$45.71	9.815%	$50.1964	$50.20	$50.20	$50.20
Purchase #4	$179.62	9.279%	$196.2869	$196.29	$196.30	$196.30
Purchase #5	$164.54	12.673%	$185.3922	$185.39	$185.40	$185.40
Purchase #6	$70.46	11.597%	$78.6312	$78.63	$78.65	$78.60
Purchase #7	$203.78	7.134%	$218.3177	$218.32	$218.30	$218.30
7 purchase totals =	$911.40		$994.6828	$994.69	$994.70	$994.60