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	$222.55	8.757%	$242.0387	$242.04	$242.05	$242.00
Purchase #2	$213.73	3.807%	$221.8667	$221.87	$221.85	$221.90
Purchase #3	$54.75	9.283%	$59.8324	$59.83	$59.85	$59.80
Purchase #4	$109.32	10.811%	$121.1386	$121.14	$121.15	$121.10
Purchase #5	$85.73	3.863%	$89.0417	$89.04	$89.05	$89.00
Purchase #6	$72.91	12.831%	$82.2651	$82.27	$82.25	$82.30
Purchase #7	$23.79	12.368%	$26.7323	$26.73	$26.75	$26.70
7 purchase totals =	$782.78		$842.9155	$842.92	$842.95	$842.80