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	$234.89	3.827%	$243.8792	$243.88	$243.90	$243.90
Purchase #2	$159.36	7.585%	$171.4475	$171.45	$171.45	$171.40
Purchase #3	$18.26	10.199%	$20.1223	$20.12	$20.10	$20.10
Purchase #4	$51.28	12.494%	$57.6869	$57.69	$57.70	$57.70
Purchase #5	$136.65	3.625%	$141.6036	$141.60	$141.60	$141.60
Purchase #6	$221.83	12.860%	$250.3573	$250.36	$250.35	$250.40
Purchase #7	$118.90	8.108%	$128.5404	$128.54	$128.55	$128.50
7 purchase totals =	$941.17		$1,013.6372	$1,013.64	$1,013.65	$1,013.60