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	$129.53	4.413%	$135.2462	$135.25	$135.25	$135.20
Purchase #2	$235.83	12.308%	$264.856	$264.86	$264.85	$264.90
Purchase #3	$128.40	8.644%	$139.4989	$139.50	$139.50	$139.50
Purchase #4	$76.88	11.307%	$85.5728	$85.57	$85.55	$85.60
Purchase #5	$95.66	8.781%	$104.0599	$104.06	$104.05	$104.10
Purchase #6	$150.94	10.850%	$167.317	$167.32	$167.30	$167.30
Purchase #7	$59.61	12.393%	$66.9975	$67.00	$67.00	$67.00
7 purchase totals =	$876.85		$963.5483	$963.56	$963.50	$963.60