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	$122.33	6.653%	$130.4686	$130.47	$130.45	$130.50
Purchase #2	$50.92	9.778%	$55.899	$55.90	$55.90	$55.90
Purchase #3	$72.77	12.841%	$82.1144	$82.11	$82.10	$82.10
Purchase #4	$29.40	3.768%	$30.5078	$30.51	$30.50	$30.50
Purchase #5	$24.59	11.502%	$27.4183	$27.42	$27.40	$27.40
Purchase #6	$67.63	7.814%	$72.9146	$72.91	$72.90	$72.90
Purchase #7	$221.97	4.353%	$231.6324	$231.63	$231.65	$231.60
7 purchase totals =	$589.61		$630.9551	$630.95	$630.90	$630.90