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	$192.47	3.153%	$198.5386	$198.54	$198.55	$198.50
Purchase #2	$144.52	8.344%	$156.5787	$156.58	$156.60	$156.60
Purchase #3	$120.71	13.840%	$137.4163	$137.42	$137.40	$137.40
Purchase #4	$40.76	10.748%	$45.1409	$45.14	$45.15	$45.10
Purchase #5	$91.30	10.166%	$100.5816	$100.58	$100.60	$100.60
Purchase #6	$200.28	6.439%	$213.176	$213.18	$213.20	$213.20
Purchase #7	$5.46	13.507%	$6.1975	$6.20	$6.20	$6.20
7 purchase totals =	$795.50		$857.6296	$857.64	$857.70	$857.60