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	$86.75	5.747%	$91.7355	$91.74	$91.75	$91.70
Purchase #2	$53.30	6.503%	$56.7661	$56.77	$56.75	$56.80
Purchase #3	$178.72	9.545%	$195.7788	$195.78	$195.80	$195.80
Purchase #4	$95.92	5.145%	$100.8551	$100.86	$100.85	$100.90
Purchase #5	$117.41	11.585%	$131.0119	$131.01	$131.00	$131.00
Purchase #6	$93.47	5.201%	$98.3314	$98.33	$98.35	$98.30
Purchase #7	$85.77	8.251%	$92.8469	$92.85	$92.85	$92.80
7 purchase totals =	$711.34		$767.3257	$767.34	$767.35	$767.30