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	$86.76	3.708%	$89.9771	$89.98	$90.00	$90.00
Purchase #2	$196.45	8.330%	$212.8143	$212.81	$212.80	$212.80
Purchase #3	$186.30	13.742%	$211.9013	$211.90	$211.90	$211.90
Purchase #4	$84.91	6.139%	$90.1226	$90.12	$90.10	$90.10
Purchase #5	$60.61	3.294%	$62.6065	$62.61	$62.60	$62.60
Purchase #6	$205.89	10.405%	$227.3129	$227.31	$227.30	$227.30
Purchase #7	$81.86	11.719%	$91.4532	$91.45	$91.45	$91.50
7 purchase totals =	$902.78		$986.1879	$986.18	$986.15	$986.20