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	$28.59	6.111%	$30.3371	$30.34	$30.35	$30.30
Purchase #2	$79.57	3.193%	$82.1107	$82.11	$82.10	$82.10
Purchase #3	$26.96	5.589%	$28.4668	$28.47	$28.45	$28.50
Purchase #4	$140.69	3.385%	$145.4524	$145.45	$145.45	$145.50
Purchase #5	$55.54	6.558%	$59.1823	$59.18	$59.20	$59.20
Purchase #6	$49.69	6.420%	$52.8801	$52.88	$52.90	$52.90
Purchase #7	$117.50	4.238%	$122.4797	$122.48	$122.50	$122.50
7 purchase totals =	$498.54		$520.9091	$520.91	$520.95	$521.00