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	$146.70	6.270%	$155.8981	$155.90	$155.90	$155.90
Purchase #2	$73.65	6.306%	$78.2944	$78.29	$78.30	$78.30
Purchase #3	$174.47	6.715%	$186.1857	$186.19	$186.20	$186.20
Purchase #4	$131.57	8.658%	$142.9613	$142.96	$142.95	$143.00
Purchase #5	$223.33	9.431%	$244.3923	$244.39	$244.40	$244.40
Purchase #6	$178.75	5.146%	$187.9485	$187.95	$187.95	$187.90
Purchase #7	$91.74	13.210%	$103.8589	$103.86	$103.85	$103.90
7 purchase totals =	$1,020.21		$1,099.5392	$1,099.54	$1,099.55	$1,099.60