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	$99.91	4.230%	$104.1362	$104.14	$104.15	$104.10
Purchase #2	$130.91	9.470%	$143.3072	$143.31	$143.30	$143.30
Purchase #3	$5.41	13.265%	$6.1276	$6.13	$6.15	$6.10
Purchase #4	$150.38	13.416%	$170.555	$170.56	$170.55	$170.60
Purchase #5	$59.88	13.443%	$67.9297	$67.93	$67.95	$67.90
Purchase #6	$155.94	10.244%	$171.9145	$171.91	$171.90	$171.90
Purchase #7	$81.26	5.682%	$85.8772	$85.88	$85.90	$85.90
7 purchase totals =	$683.69		$749.8474	$749.86	$749.90	$749.80