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	$104.32	9.782%	$114.5246	$114.52	$114.50	$114.50
Purchase #2	$172.57	9.424%	$188.833	$188.83	$188.85	$188.80
Purchase #3	$47.74	11.391%	$53.1781	$53.18	$53.20	$53.20
Purchase #4	$153.97	13.410%	$174.6174	$174.62	$174.60	$174.60
Purchase #5	$74.25	11.151%	$82.5296	$82.53	$82.55	$82.50
Purchase #6	$185.34	6.862%	$198.058	$198.06	$198.05	$198.10
Purchase #7	$96.42	13.444%	$109.3827	$109.38	$109.40	$109.40
7 purchase totals =	$834.61		$921.1234	$921.12	$921.15	$921.10