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	$198.40	5.512%	$209.3358	$209.34	$209.35	$209.30
Purchase #2	$46.77	13.229%	$52.9572	$52.96	$52.95	$53.00
Purchase #3	$228.71	5.166%	$240.5252	$240.53	$240.55	$240.50
Purchase #4	$14.43	9.699%	$15.8296	$15.83	$15.85	$15.80
Purchase #5	$145.84	9.562%	$159.7852	$159.79	$159.80	$159.80
Purchase #6	$127.88	11.461%	$142.5363	$142.54	$142.55	$142.50
Purchase #7	$83.37	8.278%	$90.2714	$90.27	$90.25	$90.30
7 purchase totals =	$845.40		$911.2407	$911.26	$911.30	$911.20