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	$90.51	11.148%	$100.6001	$100.60	$100.60	$100.60
Purchase #2	$100.53	6.289%	$106.8523	$106.85	$106.85	$106.90
Purchase #3	$219.33	12.458%	$246.6541	$246.65	$246.65	$246.70
Purchase #4	$142.45	12.866%	$160.7776	$160.78	$160.80	$160.80
Purchase #5	$17.31	8.270%	$18.7415	$18.74	$18.75	$18.70
Purchase #6	$124.56	13.142%	$140.9297	$140.93	$140.95	$140.90
Purchase #7	$242.54	10.689%	$268.4651	$268.47	$268.45	$268.50
7 purchase totals =	$937.23		$1,043.0204	$1,043.02	$1,043.05	$1,043.10