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	$86.46	7.337%	$92.8036	$92.80	$92.80	$92.80
Purchase #2	$112.56	10.318%	$124.1739	$124.17	$124.15	$124.20
Purchase #3	$241.89	9.343%	$264.4898	$264.49	$264.50	$264.50
Purchase #4	$7.74	8.823%	$8.4229	$8.42	$8.40	$8.40
Purchase #5	$41.70	8.454%	$45.2253	$45.23	$45.25	$45.20
Purchase #6	$148.25	5.481%	$156.3756	$156.38	$156.40	$156.40
Purchase #7	$37.48	12.379%	$42.1196	$42.12	$42.10	$42.10
7 purchase totals =	$676.08		$733.6107	$733.61	$733.60	$733.60