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	$75.52	11.182%	$83.9646	$83.96	$83.95	$84.00
Purchase #2	$104.41	4.563%	$109.1742	$109.17	$109.15	$109.20
Purchase #3	$91.95	8.230%	$99.5175	$99.52	$99.50	$99.50
Purchase #4	$238.96	13.207%	$270.5194	$270.52	$270.50	$270.50
Purchase #5	$84.28	6.418%	$89.6891	$89.69	$89.70	$89.70
Purchase #6	$95.33	13.809%	$108.4941	$108.49	$108.50	$108.50
Purchase #7	$5.31	13.289%	$6.0156	$6.02	$6.00	$6.00
7 purchase totals =	$695.76		$767.3745	$767.37	$767.30	$767.40