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	$168.69	3.389%	$174.4069	$174.41	$174.40	$174.40
Purchase #2	$248.33	11.400%	$276.6396	$276.64	$276.65	$276.60
Purchase #3	$90.88	10.689%	$100.5942	$100.59	$100.60	$100.60
Purchase #4	$184.60	12.441%	$207.5661	$207.57	$207.55	$207.60
Purchase #5	$100.37	10.616%	$111.0253	$111.03	$111.05	$111.00
Purchase #6	$79.64	11.311%	$88.6481	$88.65	$88.65	$88.60
Purchase #7	$42.41	10.498%	$46.8622	$46.86	$46.85	$46.90
7 purchase totals =	$914.92		$1,005.7424	$1,005.75	$1,005.75	$1,005.70