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	$222.85	8.841%	$242.5522	$242.55	$242.55	$242.60
Purchase #2	$35.95	11.801%	$40.1925	$40.19	$40.20	$40.20
Purchase #3	$70.36	3.155%	$72.5799	$72.58	$72.60	$72.60
Purchase #4	$73.51	10.635%	$81.3278	$81.33	$81.35	$81.30
Purchase #5	$150.35	6.191%	$159.6582	$159.66	$159.65	$159.70
Purchase #6	$142.37	8.526%	$154.5085	$154.51	$154.50	$154.50
Purchase #7	$89.30	5.418%	$94.1383	$94.14	$94.15	$94.10
7 purchase totals =	$784.69		$844.9574	$844.96	$845.00	$845.00