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	$250.69	9.351%	$274.132	$274.13	$274.15	$274.10
Purchase #2	$182.62	9.585%	$200.1241	$200.12	$200.10	$200.10
Purchase #3	$49.84	5.696%	$52.6789	$52.68	$52.70	$52.70
Purchase #4	$159.93	5.498%	$168.723	$168.72	$168.70	$168.70
Purchase #5	$93.42	8.602%	$101.456	$101.46	$101.45	$101.50
Purchase #6	$41.40	5.144%	$43.5296	$43.53	$43.55	$43.50
Purchase #7	$51.48	3.470%	$53.2664	$53.27	$53.25	$53.30
7 purchase totals =	$829.38		$893.9100	$893.91	$893.90	$893.90