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	$78.80	13.443%	$89.3931	$89.39	$89.40	$89.40
Purchase #2	$39.76	10.489%	$43.9304	$43.93	$43.95	$43.90
Purchase #3	$223.63	8.669%	$243.0165	$243.02	$243.00	$243.00
Purchase #4	$208.80	12.374%	$234.6369	$234.64	$234.65	$234.60
Purchase #5	$130.64	10.169%	$143.9248	$143.92	$143.90	$143.90
Purchase #6	$93.36	7.475%	$100.3387	$100.34	$100.35	$100.30
Purchase #7	$228.47	5.871%	$241.8835	$241.88	$241.90	$241.90
7 purchase totals =	$1,003.46		$1,097.1239	$1,097.12	$1,097.15	$1,097.00