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	$247.76	4.668%	$259.3254	$259.33	$259.35	$259.30
Purchase #2	$163.69	11.194%	$182.0135	$182.01	$182.00	$182.00
Purchase #3	$248.71	11.652%	$277.6897	$277.69	$277.70	$277.70
Purchase #4	$41.72	12.673%	$47.0072	$47.01	$47.00	$47.00
Purchase #5	$68.92	13.437%	$78.1808	$78.18	$78.20	$78.20
Purchase #6	$212.85	4.609%	$222.6603	$222.66	$222.65	$222.70
Purchase #7	$79.79	12.582%	$89.8292	$89.83	$89.85	$89.80
7 purchase totals =	$1,063.44		$1,156.7061	$1,156.71	$1,156.75	$1,156.70