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	$96.64	6.817%	$103.2279	$103.23	$103.25	$103.20
Purchase #2	$182.76	13.715%	$207.8255	$207.83	$207.85	$207.80
Purchase #3	$115.69	10.704%	$128.0735	$128.07	$128.05	$128.10
Purchase #4	$36.59	11.592%	$40.8315	$40.83	$40.85	$40.80
Purchase #5	$89.56	11.224%	$99.6122	$99.61	$99.60	$99.60
Purchase #6	$68.90	6.783%	$73.5735	$73.57	$73.55	$73.60
Purchase #7	$104.75	5.607%	$110.6233	$110.62	$110.60	$110.60
7 purchase totals =	$694.89		$763.7674	$763.76	$763.75	$763.70