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	$142.88	6.502%	$152.1701	$152.17	$152.15	$152.20
Purchase #2	$51.97	10.496%	$57.4248	$57.42	$57.40	$57.40
Purchase #3	$53.47	13.738%	$60.8157	$60.82	$60.80	$60.80
Purchase #4	$137.56	7.412%	$147.7559	$147.76	$147.75	$147.80
Purchase #5	$99.75	3.587%	$103.328	$103.33	$103.35	$103.30
Purchase #6	$133.73	5.429%	$140.9902	$140.99	$141.00	$141.00
Purchase #7	$231.91	10.102%	$255.3375	$255.34	$255.35	$255.30
7 purchase totals =	$851.27		$917.8222	$917.83	$917.80	$917.80