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	$209.89	6.439%	$223.4048	$223.40	$223.40	$223.40
Purchase #2	$139.75	3.431%	$144.5448	$144.54	$144.55	$144.50
Purchase #3	$149.39	12.140%	$167.5259	$167.53	$167.55	$167.50
Purchase #4	$234.41	9.681%	$257.1032	$257.10	$257.10	$257.10
Purchase #5	$72.89	10.303%	$80.3999	$80.40	$80.40	$80.40
Purchase #6	$85.69	3.846%	$88.9856	$88.99	$89.00	$89.00
Purchase #7	$42.81	7.404%	$45.9797	$45.98	$46.00	$46.00
7 purchase totals =	$934.83		$1,007.9439	$1,007.94	$1,008.00	$1,007.90