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	$83.62	7.402%	$89.8096	$89.81	$89.80	$89.80
Purchase #2	$35.56	12.689%	$40.0722	$40.07	$40.05	$40.10
Purchase #3	$36.82	13.683%	$41.8581	$41.86	$41.85	$41.90
Purchase #4	$126.72	5.724%	$133.9735	$133.97	$133.95	$134.00
Purchase #5	$168.99	13.515%	$191.829	$191.83	$191.85	$191.80
Purchase #6	$111.76	10.537%	$123.5362	$123.54	$123.55	$123.50
Purchase #7	$175.46	13.539%	$199.2155	$199.22	$199.20	$199.20
7 purchase totals =	$738.93		$820.2941	$820.30	$820.25	$820.30