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	$139.34	12.526%	$156.7937	$156.79	$156.80	$156.80
Purchase #2	$131.73	7.468%	$141.5676	$141.57	$141.55	$141.60
Purchase #3	$36.79	6.610%	$39.2218	$39.22	$39.20	$39.20
Purchase #4	$238.31	9.755%	$261.5571	$261.56	$261.55	$261.60
Purchase #5	$69.87	9.185%	$76.2876	$76.29	$76.30	$76.30
Purchase #6	$82.32	8.413%	$89.2456	$89.25	$89.25	$89.20
Purchase #7	$37.59	7.746%	$40.5017	$40.50	$40.50	$40.50
7 purchase totals =	$735.95		$805.1751	$805.18	$805.15	$805.20