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	$138.85	5.167%	$146.0244	$146.02	$146.00	$146.00
Purchase #2	$245.94	9.442%	$269.1617	$269.16	$269.15	$269.20
Purchase #3	$68.42	9.160%	$74.6873	$74.69	$74.70	$74.70
Purchase #4	$7.37	6.384%	$7.8405	$7.84	$7.85	$7.80
Purchase #5	$229.64	12.790%	$259.011	$259.01	$259.00	$259.00
Purchase #6	$209.89	7.128%	$224.851	$224.85	$224.85	$224.90
Purchase #7	$154.43	9.374%	$168.9063	$168.91	$168.90	$168.90
7 purchase totals =	$1,054.54		$1,150.4822	$1,150.48	$1,150.45	$1,150.50