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	$17.31	8.667%	$18.8103	$18.81	$18.80	$18.80
Purchase #2	$249.44	4.684%	$261.1238	$261.12	$261.10	$261.10
Purchase #3	$210.76	13.349%	$238.8944	$238.89	$238.90	$238.90
Purchase #4	$94.43	10.520%	$104.364	$104.36	$104.35	$104.40
Purchase #5	$84.54	11.137%	$93.9552	$93.96	$93.95	$94.00
Purchase #6	$47.55	9.597%	$52.1134	$52.11	$52.10	$52.10
Purchase #7	$196.57	6.649%	$209.6399	$209.64	$209.65	$209.60
7 purchase totals =	$900.60		$978.9010	$978.89	$978.85	$978.90