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	$92.37	8.870%	$100.5632	$100.56	$100.55	$100.60
Purchase #2	$68.28	3.279%	$70.5189	$70.52	$70.50	$70.50
Purchase #3	$6.44	13.846%	$7.3317	$7.33	$7.35	$7.30
Purchase #4	$35.50	6.586%	$37.838	$37.84	$37.85	$37.80
Purchase #5	$127.44	9.715%	$139.8208	$139.82	$139.80	$139.80
Purchase #6	$72.79	5.558%	$76.8357	$76.84	$76.85	$76.80
Purchase #7	$180.44	10.534%	$199.4475	$199.45	$199.45	$199.40
7 purchase totals =	$583.26		$632.3558	$632.36	$632.35	$632.20