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	$143.51	8.787%	$156.1202	$156.12	$156.10	$156.10
Purchase #2	$130.88	7.401%	$140.5664	$140.57	$140.55	$140.60
Purchase #3	$8.36	11.603%	$9.33	$9.33	$9.35	$9.30
Purchase #4	$90.64	11.401%	$100.9739	$100.97	$100.95	$101.00
Purchase #5	$42.91	11.614%	$47.8936	$47.89	$47.90	$47.90
Purchase #6	$80.68	9.195%	$88.0985	$88.10	$88.10	$88.10
Purchase #7	$33.88	9.577%	$37.1247	$37.12	$37.10	$37.10
7 purchase totals =	$530.86		$580.1073	$580.10	$580.05	$580.10