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	$186.73	3.451%	$193.1741	$193.17	$193.15	$193.20
Purchase #2	$170.34	12.270%	$191.2407	$191.24	$191.25	$191.20
Purchase #3	$174.98	8.540%	$189.9233	$189.92	$189.90	$189.90
Purchase #4	$112.62	12.799%	$127.0342	$127.03	$127.05	$127.00
Purchase #5	$185.94	10.611%	$205.6701	$205.67	$205.65	$205.70
Purchase #6	$30.69	10.362%	$33.8701	$33.87	$33.85	$33.90
Purchase #7	$53.48	3.817%	$55.5213	$55.52	$55.50	$55.50
7 purchase totals =	$914.78		$996.4338	$996.42	$996.35	$996.40