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	$160.50	7.256%	$172.1459	$172.15	$172.15	$172.10
Purchase #2	$67.53	13.758%	$76.8208	$76.82	$76.80	$76.80
Purchase #3	$165.33	9.746%	$181.4431	$181.44	$181.45	$181.40
Purchase #4	$57.90	4.619%	$60.5744	$60.57	$60.55	$60.60
Purchase #5	$199.92	6.813%	$213.5405	$213.54	$213.55	$213.50
Purchase #6	$167.75	12.381%	$188.5191	$188.52	$188.50	$188.50
Purchase #7	$77.36	3.835%	$80.3268	$80.33	$80.35	$80.30
7 purchase totals =	$896.29		$973.3706	$973.37	$973.35	$973.20