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	$85.76	4.666%	$89.7616	$89.76	$89.75	$89.80
Purchase #2	$135.88	9.531%	$148.8307	$148.83	$148.85	$148.80
Purchase #3	$175.37	8.866%	$190.9183	$190.92	$190.90	$190.90
Purchase #4	$114.25	4.203%	$119.0519	$119.05	$119.05	$119.10
Purchase #5	$67.61	5.809%	$71.5375	$71.54	$71.55	$71.50
Purchase #6	$111.82	12.402%	$125.6879	$125.69	$125.70	$125.70
Purchase #7	$81.42	13.589%	$92.4842	$92.48	$92.50	$92.50
7 purchase totals =	$772.11		$838.2721	$838.27	$838.30	$838.30