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	$79.77	11.817%	$89.1964	$89.20	$89.20	$89.20
Purchase #2	$83.60	6.467%	$89.0064	$89.01	$89.00	$89.00
Purchase #3	$166.65	12.489%	$187.4629	$187.46	$187.45	$187.50
Purchase #4	$72.84	11.299%	$81.0702	$81.07	$81.05	$81.10
Purchase #5	$157.84	6.206%	$167.6356	$167.64	$167.65	$167.60
Purchase #6	$22.77	7.653%	$24.5126	$24.51	$24.50	$24.50
Purchase #7	$64.67	5.259%	$68.071	$68.07	$68.05	$68.10
7 purchase totals =	$648.14		$706.9551	$706.96	$706.90	$707.00