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	$121.63	8.304%	$131.7302	$131.73	$131.75	$131.70
Purchase #2	$229.85	11.189%	$255.5679	$255.57	$255.55	$255.60
Purchase #3	$119.36	7.370%	$128.1568	$128.16	$128.15	$128.20
Purchase #4	$125.53	11.440%	$139.8906	$139.89	$139.90	$139.90
Purchase #5	$229.66	3.632%	$238.0013	$238.00	$238.00	$238.00
Purchase #6	$21.78	12.461%	$24.494	$24.49	$24.50	$24.50
Purchase #7	$84.56	11.859%	$94.588	$94.59	$94.60	$94.60
7 purchase totals =	$932.37		$1,012.4288	$1,012.43	$1,012.45	$1,012.50