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	$70.48	11.364%	$78.4893	$78.49	$78.50	$78.50
Purchase #2	$210.43	13.850%	$239.5746	$239.57	$239.55	$239.60
Purchase #3	$81.48	10.197%	$89.7885	$89.79	$89.80	$89.80
Purchase #4	$165.27	11.147%	$183.6926	$183.69	$183.70	$183.70
Purchase #5	$229.93	7.211%	$246.5103	$246.51	$246.50	$246.50
Purchase #6	$152.90	13.839%	$174.0598	$174.06	$174.05	$174.10
Purchase #7	$131.87	12.780%	$148.723	$148.72	$148.70	$148.70
7 purchase totals =	$1,042.36		$1,160.8381	$1,160.83	$1,160.80	$1,160.90