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	$123.72	9.449%	$135.4103	$135.41	$135.40	$135.40
Purchase #2	$205.38	12.705%	$231.4735	$231.47	$231.45	$231.50
Purchase #3	$167.27	7.251%	$179.3987	$179.40	$179.40	$179.40
Purchase #4	$231.61	7.563%	$249.1267	$249.13	$249.15	$249.10
Purchase #5	$54.57	13.433%	$61.9004	$61.90	$61.90	$61.90
Purchase #6	$39.79	6.866%	$42.522	$42.52	$42.50	$42.50
Purchase #7	$191.85	10.215%	$211.4475	$211.45	$211.45	$211.40
7 purchase totals =	$1,014.19		$1,111.2791	$1,111.28	$1,111.25	$1,111.20