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	$230.61	5.626%	$243.5841	$243.58	$243.60	$243.60
Purchase #2	$79.47	5.122%	$83.5405	$83.54	$83.55	$83.50
Purchase #3	$63.27	11.472%	$70.5283	$70.53	$70.55	$70.50
Purchase #4	$77.80	13.782%	$88.5224	$88.52	$88.50	$88.50
Purchase #5	$180.98	4.828%	$189.7177	$189.72	$189.70	$189.70
Purchase #6	$72.89	9.459%	$79.7847	$79.78	$79.80	$79.80
Purchase #7	$104.33	4.326%	$108.8433	$108.84	$108.85	$108.80
7 purchase totals =	$809.35		$864.5210	$864.51	$864.55	$864.40