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	$94.55	13.779%	$107.578	$107.58	$107.60	$107.60
Purchase #2	$168.96	9.699%	$185.3474	$185.35	$185.35	$185.30
Purchase #3	$64.76	13.598%	$73.5661	$73.57	$73.55	$73.60
Purchase #4	$119.46	11.647%	$133.3735	$133.37	$133.35	$133.40
Purchase #5	$55.92	13.520%	$63.4804	$63.48	$63.50	$63.50
Purchase #6	$82.73	11.502%	$92.2456	$92.25	$92.25	$92.20
Purchase #7	$10.28	4.765%	$10.7698	$10.77	$10.75	$10.80
7 purchase totals =	$596.66		$666.3608	$666.37	$666.35	$666.40