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	$128.26	13.403%	$145.4507	$145.45	$145.45	$145.50
Purchase #2	$110.40	13.359%	$125.1483	$125.15	$125.15	$125.10
Purchase #3	$90.34	9.710%	$99.112	$99.11	$99.10	$99.10
Purchase #4	$179.87	9.168%	$196.3605	$196.36	$196.35	$196.40
Purchase #5	$91.52	10.158%	$100.8166	$100.82	$100.80	$100.80
Purchase #6	$44.89	11.228%	$49.9302	$49.93	$49.95	$49.90
Purchase #7	$84.47	9.377%	$92.3908	$92.39	$92.40	$92.40
7 purchase totals =	$729.75		$809.2091	$809.21	$809.20	$809.20