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	$64.49	11.849%	$72.1314	$72.13	$72.15	$72.10
Purchase #2	$87.83	12.670%	$98.9581	$98.96	$98.95	$99.00
Purchase #3	$82.33	5.605%	$86.9446	$86.94	$86.95	$86.90
Purchase #4	$164.32	9.721%	$180.2935	$180.29	$180.30	$180.30
Purchase #5	$80.56	10.718%	$89.1944	$89.19	$89.20	$89.20
Purchase #6	$144.50	10.109%	$159.1075	$159.11	$159.10	$159.10
Purchase #7	$213.57	3.514%	$221.0748	$221.07	$221.05	$221.10
7 purchase totals =	$837.60		$907.7043	$907.69	$907.70	$907.70