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	$168.76	6.696%	$180.0602	$180.06	$180.05	$180.10
Purchase #2	$62.99	3.387%	$65.1235	$65.12	$65.10	$65.10
Purchase #3	$47.73	12.622%	$53.7545	$53.75	$53.75	$53.80
Purchase #4	$82.37	3.323%	$85.1072	$85.11	$85.10	$85.10
Purchase #5	$174.58	9.717%	$191.5439	$191.54	$191.55	$191.50
Purchase #6	$79.76	13.291%	$90.3609	$90.36	$90.35	$90.40
Purchase #7	$166.46	3.501%	$172.2878	$172.29	$172.30	$172.30
7 purchase totals =	$782.65		$838.2380	$838.23	$838.20	$838.30