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	$204.29	5.380%	$215.2808	$215.28	$215.30	$215.30
Purchase #2	$115.81	10.574%	$128.0557	$128.06	$128.05	$128.10
Purchase #3	$34.90	8.414%	$37.8365	$37.84	$37.85	$37.80
Purchase #4	$31.50	11.581%	$35.148	$35.15	$35.15	$35.10
Purchase #5	$165.36	10.432%	$182.6104	$182.61	$182.60	$182.60
Purchase #6	$19.69	5.224%	$20.7186	$20.72	$20.70	$20.70
Purchase #7	$184.43	3.386%	$190.6748	$190.67	$190.65	$190.70
7 purchase totals =	$755.98		$810.3248	$810.33	$810.30	$810.30