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	$19.81	7.205%	$21.2373	$21.24	$21.25	$21.20
Purchase #2	$150.84	11.662%	$168.431	$168.43	$168.45	$168.40
Purchase #3	$194.31	11.851%	$217.3377	$217.34	$217.35	$217.30
Purchase #4	$89.74	5.419%	$94.603	$94.60	$94.60	$94.60
Purchase #5	$26.42	7.232%	$28.3307	$28.33	$28.35	$28.30
Purchase #6	$242.81	13.653%	$275.9608	$275.96	$275.95	$276.00
Purchase #7	$88.46	3.559%	$91.6083	$91.61	$91.60	$91.60
7 purchase totals =	$812.39		$897.5088	$897.51	$897.55	$897.40