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	$47.47	8.822%	$51.6578	$51.66	$51.65	$51.70
Purchase #2	$136.71	11.490%	$152.418	$152.42	$152.40	$152.40
Purchase #3	$101.82	6.511%	$108.4495	$108.45	$108.45	$108.40
Purchase #4	$143.48	9.234%	$156.7289	$156.73	$156.75	$156.70
Purchase #5	$146.76	8.352%	$159.0174	$159.02	$159.00	$159.00
Purchase #6	$221.56	13.245%	$250.9056	$250.91	$250.90	$250.90
Purchase #7	$182.62	9.435%	$199.8502	$199.85	$199.85	$199.90
7 purchase totals =	$980.42		$1,079.0274	$1,079.04	$1,079.00	$1,079.00