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	$78.96	5.182%	$83.0517	$83.05	$83.05	$83.10
Purchase #2	$75.84	3.199%	$78.2661	$78.27	$78.25	$78.30
Purchase #3	$35.49	8.196%	$38.3988	$38.40	$38.40	$38.40
Purchase #4	$171.53	4.230%	$178.7857	$178.79	$178.80	$178.80
Purchase #5	$147.93	7.300%	$158.7289	$158.73	$158.75	$158.70
Purchase #6	$63.56	3.846%	$66.0045	$66.00	$66.00	$66.00
Purchase #7	$131.76	7.857%	$142.1124	$142.11	$142.10	$142.10
7 purchase totals =	$705.07		$745.3481	$745.35	$745.35	$745.40