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	$121.84	3.360%	$125.9338	$125.93	$125.95	$125.90
Purchase #2	$169.85	8.734%	$184.6847	$184.68	$184.70	$184.70
Purchase #3	$76.38	11.676%	$85.2981	$85.30	$85.30	$85.30
Purchase #4	$56.76	4.488%	$59.3074	$59.31	$59.30	$59.30
Purchase #5	$73.61	3.669%	$76.3108	$76.31	$76.30	$76.30
Purchase #6	$102.30	9.246%	$111.7587	$111.76	$111.75	$111.80
Purchase #7	$185.64	6.819%	$198.2988	$198.30	$198.30	$198.30
7 purchase totals =	$786.38		$841.5923	$841.59	$841.60	$841.60