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	$82.81	8.350%	$89.7246	$89.72	$89.70	$89.70
Purchase #2	$132.63	10.557%	$146.6317	$146.63	$146.65	$146.60
Purchase #3	$179.82	11.408%	$200.3339	$200.33	$200.35	$200.30
Purchase #4	$59.96	6.162%	$63.6547	$63.65	$63.65	$63.70
Purchase #5	$11.55	8.419%	$12.5224	$12.52	$12.50	$12.50
Purchase #6	$211.56	4.275%	$220.6042	$220.60	$220.60	$220.60
Purchase #7	$199.32	6.676%	$212.6266	$212.63	$212.65	$212.60
7 purchase totals =	$877.65		$946.0981	$946.08	$946.10	$946.00