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	$18.91	5.663%	$19.9809	$19.98	$20.00	$20.00
Purchase #2	$162.70	7.199%	$174.4128	$174.41	$174.40	$174.40
Purchase #3	$165.79	7.444%	$178.1314	$178.13	$178.15	$178.10
Purchase #4	$55.96	11.381%	$62.3288	$62.33	$62.35	$62.30
Purchase #5	$250.80	7.850%	$270.4878	$270.49	$270.50	$270.50
Purchase #6	$67.61	6.286%	$71.86	$71.86	$71.85	$71.90
Purchase #7	$175.61	8.618%	$190.7441	$190.74	$190.75	$190.70
7 purchase totals =	$897.38		$967.9458	$967.94	$968.00	$967.90