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	$243.90	11.471%	$271.8778	$271.88	$271.90	$271.90
Purchase #2	$194.30	7.834%	$209.5215	$209.52	$209.50	$209.50
Purchase #3	$13.32	10.425%	$14.7086	$14.71	$14.70	$14.70
Purchase #4	$86.60	3.736%	$89.8354	$89.84	$89.85	$89.80
Purchase #5	$187.41	7.525%	$201.5126	$201.51	$201.50	$201.50
Purchase #6	$55.83	6.526%	$59.4735	$59.47	$59.45	$59.50
Purchase #7	$219.29	10.867%	$243.1202	$243.12	$243.10	$243.10
7 purchase totals =	$1,000.65		$1,090.0496	$1,090.05	$1,090.00	$1,090.00