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	$61.69	7.484%	$66.3069	$66.31	$66.30	$66.30
Purchase #2	$123.39	6.575%	$131.5029	$131.50	$131.50	$131.50
Purchase #3	$233.46	7.539%	$251.0605	$251.06	$251.05	$251.10
Purchase #4	$43.96	6.395%	$46.7712	$46.77	$46.75	$46.80
Purchase #5	$245.90	9.280%	$268.7195	$268.72	$268.70	$268.70
Purchase #6	$33.51	6.369%	$35.6443	$35.64	$35.65	$35.60
Purchase #7	$8.57	3.728%	$8.8895	$8.89	$8.90	$8.90
7 purchase totals =	$750.48		$808.8948	$808.89	$808.85	$808.90