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	$80.34	5.819%	$85.015	$85.02	$85.00	$85.00
Purchase #2	$190.88	13.638%	$216.9122	$216.91	$216.90	$216.90
Purchase #3	$62.55	3.632%	$64.8218	$64.82	$64.80	$64.80
Purchase #4	$41.78	12.646%	$47.0635	$47.06	$47.05	$47.10
Purchase #5	$63.97	12.827%	$72.1754	$72.18	$72.20	$72.20
Purchase #6	$125.79	11.573%	$140.3477	$140.35	$140.35	$140.30
Purchase #7	$50.39	3.811%	$52.3104	$52.31	$52.30	$52.30
7 purchase totals =	$615.70		$678.6460	$678.65	$678.60	$678.60