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	$6.68	13.555%	$7.5855	$7.59	$7.60	$7.60
Purchase #2	$236.40	7.749%	$254.7186	$254.72	$254.70	$254.70
Purchase #3	$198.59	7.481%	$213.4465	$213.45	$213.45	$213.40
Purchase #4	$185.89	3.246%	$191.924	$191.92	$191.90	$191.90
Purchase #5	$170.89	11.494%	$190.5321	$190.53	$190.55	$190.50
Purchase #6	$50.33	8.144%	$54.4289	$54.43	$54.45	$54.40
Purchase #7	$191.71	9.691%	$210.2886	$210.29	$210.30	$210.30
7 purchase totals =	$1,040.49		$1,122.9242	$1,122.93	$1,122.95	$1,122.80