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	$5.55	13.588%	$6.3041	$6.30	$6.30	$6.30
Purchase #2	$80.82	5.208%	$85.0291	$85.03	$85.05	$85.00
Purchase #3	$93.47	3.472%	$96.7153	$96.72	$96.70	$96.70
Purchase #4	$242.72	3.589%	$251.4312	$251.43	$251.45	$251.40
Purchase #5	$69.26	3.319%	$71.5587	$71.56	$71.55	$71.60
Purchase #6	$66.77	6.537%	$71.1348	$71.13	$71.15	$71.10
Purchase #7	$103.77	7.474%	$111.5258	$111.53	$111.55	$111.50
7 purchase totals =	$662.36		$693.6990	$693.70	$693.75	$693.60