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	$150.56	12.188%	$168.9103	$168.91	$168.90	$168.90
Purchase #2	$51.40	8.290%	$55.6611	$55.66	$55.65	$55.70
Purchase #3	$68.77	7.451%	$73.8941	$73.89	$73.90	$73.90
Purchase #4	$48.85	10.275%	$53.8693	$53.87	$53.85	$53.90
Purchase #5	$197.82	6.374%	$210.429	$210.43	$210.45	$210.40
Purchase #6	$140.62	5.333%	$148.1193	$148.12	$148.10	$148.10
Purchase #7	$102.63	10.347%	$113.2491	$113.25	$113.25	$113.20
7 purchase totals =	$760.65		$824.1322	$824.13	$824.10	$824.10