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	$79.76	11.577%	$88.9938	$88.99	$89.00	$89.00
Purchase #2	$97.29	12.376%	$109.3306	$109.33	$109.35	$109.30
Purchase #3	$100.73	13.295%	$114.1221	$114.12	$114.10	$114.10
Purchase #4	$143.99	5.796%	$152.3357	$152.34	$152.35	$152.30
Purchase #5	$144.61	13.747%	$164.4895	$164.49	$164.50	$164.50
Purchase #6	$67.64	12.512%	$76.1031	$76.10	$76.10	$76.10
Purchase #7	$116.86	11.333%	$130.1037	$130.10	$130.10	$130.10
7 purchase totals =	$750.88		$835.4785	$835.47	$835.50	$835.40