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	$48.40	8.414%	$52.4724	$52.47	$52.45	$52.50
Purchase #2	$106.40	12.219%	$119.401	$119.40	$119.40	$119.40
Purchase #3	$111.65	8.251%	$120.8622	$120.86	$120.85	$120.90
Purchase #4	$133.87	10.825%	$148.3614	$148.36	$148.35	$148.40
Purchase #5	$84.42	9.484%	$92.4264	$92.43	$92.45	$92.40
Purchase #6	$209.58	6.353%	$222.8946	$222.89	$222.90	$222.90
Purchase #7	$174.55	9.460%	$191.0624	$191.06	$191.05	$191.10
7 purchase totals =	$868.87		$947.4804	$947.47	$947.45	$947.60