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	$80.36	3.144%	$82.8865	$82.89	$82.90	$82.90
Purchase #2	$190.91	4.644%	$199.7759	$199.78	$199.80	$199.80
Purchase #3	$56.90	10.294%	$62.7573	$62.76	$62.75	$62.80
Purchase #4	$135.38	4.370%	$141.2961	$141.30	$141.30	$141.30
Purchase #5	$59.42	11.618%	$66.3234	$66.32	$66.30	$66.30
Purchase #6	$191.70	4.531%	$200.3859	$200.39	$200.40	$200.40
Purchase #7	$136.73	9.220%	$149.3365	$149.34	$149.35	$149.30
7 purchase totals =	$851.40		$902.7616	$902.78	$902.80	$902.80