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	$90.49	10.315%	$99.824	$99.82	$99.80	$99.80
Purchase #2	$45.82	12.481%	$51.5388	$51.54	$51.55	$51.50
Purchase #3	$245.84	6.730%	$262.385	$262.39	$262.40	$262.40
Purchase #4	$83.34	9.874%	$91.569	$91.57	$91.55	$91.60
Purchase #5	$168.63	12.123%	$189.073	$189.07	$189.05	$189.10
Purchase #6	$124.58	4.777%	$130.5312	$130.53	$130.55	$130.50
Purchase #7	$50.64	7.755%	$54.5671	$54.57	$54.55	$54.60
7 purchase totals =	$809.34		$879.4881	$879.49	$879.45	$879.50