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	$203.79	12.484%	$229.2311	$229.23	$229.25	$229.20
Purchase #2	$134.49	7.249%	$144.2392	$144.24	$144.25	$144.20
Purchase #3	$148.91	6.529%	$158.6323	$158.63	$158.65	$158.60
Purchase #4	$91.61	11.646%	$102.2789	$102.28	$102.30	$102.30
Purchase #5	$79.51	12.416%	$89.382	$89.38	$89.40	$89.40
Purchase #6	$195.62	7.450%	$210.1937	$210.19	$210.20	$210.20
Purchase #7	$63.36	12.487%	$71.2718	$71.27	$71.25	$71.30
7 purchase totals =	$917.29		$1,005.2290	$1,005.22	$1,005.30	$1,005.20