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	$85.70	6.503%	$91.2731	$91.27	$91.25	$91.30
Purchase #2	$18.98	7.379%	$20.3805	$20.38	$20.40	$20.40
Purchase #3	$17.83	8.498%	$19.3452	$19.35	$19.35	$19.30
Purchase #4	$18.93	6.568%	$20.1733	$20.17	$20.15	$20.20
Purchase #5	$115.84	13.421%	$131.3869	$131.39	$131.40	$131.40
Purchase #6	$27.82	7.840%	$30.0011	$30.00	$30.00	$30.00
Purchase #7	$96.76	8.389%	$104.8772	$104.88	$104.90	$104.90
7 purchase totals =	$381.86		$417.4373	$417.44	$417.45	$417.50