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	$123.61	4.157%	$128.7485	$128.75	$128.75	$128.70
Purchase #2	$39.70	7.437%	$42.6525	$42.65	$42.65	$42.70
Purchase #3	$95.41	13.154%	$107.9602	$107.96	$107.95	$108.00
Purchase #4	$101.39	9.111%	$110.6276	$110.63	$110.65	$110.60
Purchase #5	$116.49	12.869%	$131.4811	$131.48	$131.50	$131.50
Purchase #6	$231.71	6.124%	$245.8999	$245.90	$245.90	$245.90
Purchase #7	$225.83	11.555%	$251.9247	$251.92	$251.90	$251.90
7 purchase totals =	$934.14		$1,019.2945	$1,019.29	$1,019.30	$1,019.30