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	$196.76	3.667%	$203.9752	$203.98	$204.00	$204.00
Purchase #2	$99.68	3.420%	$103.0891	$103.09	$103.10	$103.10
Purchase #3	$30.77	9.818%	$33.791	$33.79	$33.80	$33.80
Purchase #4	$137.37	3.354%	$141.9774	$141.98	$142.00	$142.00
Purchase #5	$95.81	4.284%	$99.9145	$99.91	$99.90	$99.90
Purchase #6	$202.54	12.623%	$228.1066	$228.11	$228.10	$228.10
Purchase #7	$73.69	6.160%	$78.2293	$78.23	$78.25	$78.20
7 purchase totals =	$836.62		$889.0831	$889.09	$889.15	$889.10