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	$80.83	9.791%	$88.7441	$88.74	$88.75	$88.70
Purchase #2	$77.42	6.843%	$82.7179	$82.72	$82.70	$82.70
Purchase #3	$88.32	11.839%	$98.7762	$98.78	$98.80	$98.80
Purchase #4	$203.75	7.571%	$219.1759	$219.18	$219.20	$219.20
Purchase #5	$219.96	6.861%	$235.0515	$235.05	$235.05	$235.10
Purchase #6	$220.82	10.417%	$243.8228	$243.82	$243.80	$243.80
Purchase #7	$105.78	5.533%	$111.6328	$111.63	$111.65	$111.60
7 purchase totals =	$996.88		$1,079.9212	$1,079.92	$1,079.95	$1,079.90