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	$100.87	11.324%	$112.2925	$112.29	$112.30	$112.30
Purchase #2	$62.56	12.170%	$70.1736	$70.17	$70.15	$70.20
Purchase #3	$229.92	6.488%	$244.8372	$244.84	$244.85	$244.80
Purchase #4	$187.63	6.269%	$199.3925	$199.39	$199.40	$199.40
Purchase #5	$83.28	5.702%	$88.0286	$88.03	$88.05	$88.00
Purchase #6	$62.69	12.518%	$70.5375	$70.54	$70.55	$70.50
Purchase #7	$82.81	7.713%	$89.1971	$89.20	$89.20	$89.20
7 purchase totals =	$809.76		$874.4590	$874.46	$874.50	$874.40