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	$87.94	3.478%	$90.9986	$91.00	$91.00	$91.00
Purchase #2	$232.45	9.321%	$254.1167	$254.12	$254.10	$254.10
Purchase #3	$142.25	6.489%	$151.4806	$151.48	$151.50	$151.50
Purchase #4	$61.91	9.404%	$67.732	$67.73	$67.75	$67.70
Purchase #5	$35.44	5.539%	$37.403	$37.40	$37.40	$37.40
Purchase #6	$57.89	12.693%	$65.238	$65.24	$65.25	$65.20
Purchase #7	$157.90	6.674%	$168.4382	$168.44	$168.45	$168.40
7 purchase totals =	$775.78		$835.4071	$835.41	$835.45	$835.30