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	$11.53	11.543%	$12.8609	$12.86	$12.85	$12.90
Purchase #2	$55.94	10.399%	$61.7572	$61.76	$61.75	$61.80
Purchase #3	$215.48	3.506%	$223.0347	$223.03	$223.05	$223.00
Purchase #4	$9.28	12.138%	$10.4064	$10.41	$10.40	$10.40
Purchase #5	$204.92	9.219%	$223.8116	$223.81	$223.80	$223.80
Purchase #6	$28.58	9.118%	$31.1859	$31.19	$31.20	$31.20
Purchase #7	$209.37	9.755%	$229.794	$229.79	$229.80	$229.80
7 purchase totals =	$735.10		$792.8507	$792.85	$792.85	$792.90