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	$102.47	6.742%	$109.3785	$109.38	$109.40	$109.40
Purchase #2	$244.83	10.713%	$271.0586	$271.06	$271.05	$271.10
Purchase #3	$83.53	7.751%	$90.0044	$90.00	$90.00	$90.00
Purchase #4	$238.45	10.721%	$264.0142	$264.01	$264.00	$264.00
Purchase #5	$139.25	12.506%	$156.6646	$156.66	$156.65	$156.70
Purchase #6	$74.57	8.767%	$81.1076	$81.11	$81.10	$81.10
Purchase #7	$93.41	5.792%	$98.8203	$98.82	$98.80	$98.80
7 purchase totals =	$976.51		$1,071.0482	$1,071.04	$1,071.00	$1,071.10