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	$63.58	12.314%	$71.4092	$71.41	$71.40	$71.40
Purchase #2	$145.37	5.604%	$153.5165	$153.52	$153.50	$153.50
Purchase #3	$84.59	11.551%	$94.361	$94.36	$94.35	$94.40
Purchase #4	$65.33	10.734%	$72.3425	$72.34	$72.35	$72.30
Purchase #5	$47.82	10.703%	$52.9382	$52.94	$52.95	$52.90
Purchase #6	$50.62	3.478%	$52.3806	$52.38	$52.40	$52.40
Purchase #7	$79.37	3.597%	$82.2249	$82.22	$82.20	$82.20
7 purchase totals =	$536.68		$579.1729	$579.17	$579.15	$579.10