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	$78.68	13.834%	$89.5646	$89.56	$89.55	$89.60
Purchase #2	$233.70	13.384%	$264.9784	$264.98	$265.00	$265.00
Purchase #3	$126.91	5.604%	$134.022	$134.02	$134.00	$134.00
Purchase #4	$125.95	11.751%	$140.7504	$140.75	$140.75	$140.80
Purchase #5	$84.83	13.865%	$96.5917	$96.59	$96.60	$96.60
Purchase #6	$157.81	6.830%	$168.5884	$168.59	$168.60	$168.60
Purchase #7	$32.29	12.838%	$36.4354	$36.44	$36.45	$36.40
7 purchase totals =	$840.17		$930.9309	$930.93	$930.95	$931.00