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	$172.46	4.146%	$179.6102	$179.61	$179.60	$179.60
Purchase #2	$169.62	11.161%	$188.5513	$188.55	$188.55	$188.60
Purchase #3	$80.36	11.130%	$89.3041	$89.30	$89.30	$89.30
Purchase #4	$140.79	4.768%	$147.5029	$147.50	$147.50	$147.50
Purchase #5	$86.84	3.120%	$89.5494	$89.55	$89.55	$89.50
Purchase #6	$42.98	7.102%	$46.0324	$46.03	$46.05	$46.00
Purchase #7	$224.49	4.690%	$235.0186	$235.02	$235.00	$235.00
7 purchase totals =	$917.54		$975.5689	$975.56	$975.55	$975.50