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	$93.38	6.605%	$99.5477	$99.55	$99.55	$99.50
Purchase #2	$118.69	10.622%	$131.2973	$131.30	$131.30	$131.30
Purchase #3	$189.63	11.533%	$211.5	$211.50	$211.50	$211.50
Purchase #4	$77.37	6.379%	$82.3054	$82.31	$82.30	$82.30
Purchase #5	$112.49	7.719%	$121.1731	$121.17	$121.15	$121.20
Purchase #6	$91.41	6.513%	$97.3635	$97.36	$97.35	$97.40
Purchase #7	$98.42	7.245%	$105.5505	$105.55	$105.55	$105.60
7 purchase totals =	$781.39		$848.7375	$848.74	$848.70	$848.80