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	$77.72	3.400%	$80.3625	$80.36	$80.35	$80.40
Purchase #2	$72.35	9.601%	$79.2963	$79.30	$79.30	$79.30
Purchase #3	$87.65	12.536%	$98.6378	$98.64	$98.65	$98.60
Purchase #4	$176.63	9.194%	$192.8694	$192.87	$192.85	$192.90
Purchase #5	$115.59	13.789%	$131.5287	$131.53	$131.55	$131.50
Purchase #6	$210.73	5.111%	$221.5004	$221.50	$221.50	$221.50
Purchase #7	$236.27	4.411%	$246.6919	$246.69	$246.70	$246.70
7 purchase totals =	$976.94		$1,050.8870	$1,050.89	$1,050.90	$1,050.90