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	$235.55	3.544%	$243.8979	$243.90	$243.90	$243.90
Purchase #2	$57.30	9.216%	$62.5808	$62.58	$62.60	$62.60
Purchase #3	$82.39	4.109%	$85.7754	$85.78	$85.80	$85.80
Purchase #4	$52.38	8.483%	$56.8234	$56.82	$56.80	$56.80
Purchase #5	$93.32	4.118%	$97.1629	$97.16	$97.15	$97.20
Purchase #6	$79.54	12.803%	$89.7235	$89.72	$89.70	$89.70
Purchase #7	$188.39	11.636%	$210.3111	$210.31	$210.30	$210.30
7 purchase totals =	$788.87		$846.2750	$846.27	$846.25	$846.30