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	$88.46	5.671%	$93.4766	$93.48	$93.50	$93.50
Purchase #2	$131.69	8.464%	$142.8362	$142.84	$142.85	$142.80
Purchase #3	$69.80	12.327%	$78.4042	$78.40	$78.40	$78.40
Purchase #4	$25.73	12.462%	$28.9365	$28.94	$28.95	$28.90
Purchase #5	$98.61	4.601%	$103.147	$103.15	$103.15	$103.10
Purchase #6	$165.58	12.175%	$185.7394	$185.74	$185.75	$185.70
Purchase #7	$115.40	11.715%	$128.9191	$128.92	$128.90	$128.90
7 purchase totals =	$695.27		$761.4590	$761.47	$761.50	$761.30