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	$82.54	8.467%	$89.5287	$89.53	$89.55	$89.50
Purchase #2	$216.88	4.591%	$226.837	$226.84	$226.85	$226.80
Purchase #3	$247.38	6.443%	$263.3187	$263.32	$263.30	$263.30
Purchase #4	$73.63	6.794%	$78.6324	$78.63	$78.65	$78.60
Purchase #5	$154.28	9.621%	$169.1233	$169.12	$169.10	$169.10
Purchase #6	$128.82	6.130%	$136.7167	$136.72	$136.70	$136.70
Purchase #7	$245.38	5.245%	$258.2502	$258.25	$258.25	$258.30
7 purchase totals =	$1,148.91		$1,222.4070	$1,222.41	$1,222.40	$1,222.30