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	$133.49	8.552%	$144.9061	$144.91	$144.90	$144.90
Purchase #2	$82.49	13.288%	$93.4513	$93.45	$93.45	$93.50
Purchase #3	$250.78	5.823%	$265.3829	$265.38	$265.40	$265.40
Purchase #4	$27.75	13.433%	$31.4777	$31.48	$31.50	$31.50
Purchase #5	$78.44	8.783%	$85.3294	$85.33	$85.35	$85.30
Purchase #6	$52.58	11.360%	$58.5531	$58.55	$58.55	$58.60
Purchase #7	$246.65	6.866%	$263.585	$263.59	$263.60	$263.60
7 purchase totals =	$872.18		$942.6855	$942.69	$942.75	$942.80