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	$6.91	6.364%	$7.3498	$7.35	$7.35	$7.30
Purchase #2	$89.91	11.384%	$100.1454	$100.15	$100.15	$100.10
Purchase #3	$120.89	8.594%	$131.2793	$131.28	$131.30	$131.30
Purchase #4	$165.27	4.578%	$172.8361	$172.84	$172.85	$172.80
Purchase #5	$229.85	3.266%	$237.3569	$237.36	$237.35	$237.40
Purchase #6	$63.78	5.578%	$67.3376	$67.34	$67.35	$67.30
Purchase #7	$144.72	13.563%	$164.3484	$164.35	$164.35	$164.30
7 purchase totals =	$821.33		$880.6535	$880.67	$880.70	$880.50