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	$234.78	5.421%	$247.5074	$247.51	$247.50	$247.50
Purchase #2	$90.99	5.775%	$96.2447	$96.24	$96.25	$96.20
Purchase #3	$89.57	12.196%	$100.494	$100.49	$100.50	$100.50
Purchase #4	$81.73	13.824%	$93.0284	$93.03	$93.05	$93.00
Purchase #5	$152.52	11.137%	$169.5062	$169.51	$169.50	$169.50
Purchase #6	$75.39	13.705%	$85.7222	$85.72	$85.70	$85.70
Purchase #7	$16.38	10.257%	$18.0601	$18.06	$18.05	$18.10
7 purchase totals =	$741.36		$810.5630	$810.56	$810.55	$810.50