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	$236.75	13.682%	$269.1421	$269.14	$269.15	$269.10
Purchase #2	$18.75	8.222%	$20.2916	$20.29	$20.30	$20.30
Purchase #3	$39.75	6.481%	$42.3262	$42.33	$42.35	$42.30
Purchase #4	$53.38	11.119%	$59.3153	$59.32	$59.30	$59.30
Purchase #5	$31.62	6.265%	$33.601	$33.60	$33.60	$33.60
Purchase #6	$6.67	11.157%	$7.4142	$7.41	$7.40	$7.40
Purchase #7	$71.88	3.853%	$74.6495	$74.65	$74.65	$74.60
7 purchase totals =	$458.80		$506.7399	$506.74	$506.75	$506.60