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	$110.41	13.103%	$124.877	$124.88	$124.90	$124.90
Purchase #2	$39.88	6.223%	$42.3617	$42.36	$42.35	$42.40
Purchase #3	$157.77	3.249%	$162.8959	$162.90	$162.90	$162.90
Purchase #4	$71.65	12.874%	$80.8742	$80.87	$80.85	$80.90
Purchase #5	$60.31	13.340%	$68.3554	$68.36	$68.35	$68.40
Purchase #6	$189.56	10.639%	$209.7273	$209.73	$209.75	$209.70
Purchase #7	$33.64	4.831%	$35.2651	$35.27	$35.25	$35.30
7 purchase totals =	$663.22		$724.3566	$724.37	$724.35	$724.50