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	$114.27	12.115%	$128.1138	$128.11	$128.10	$128.10
Purchase #2	$95.76	12.806%	$108.023	$108.02	$108.00	$108.00
Purchase #3	$231.47	11.409%	$257.8784	$257.88	$257.90	$257.90
Purchase #4	$39.89	9.115%	$43.526	$43.53	$43.55	$43.50
Purchase #5	$222.38	9.610%	$243.7507	$243.75	$243.75	$243.80
Purchase #6	$18.27	13.151%	$20.6727	$20.67	$20.65	$20.70
Purchase #7	$250.90	5.752%	$265.3318	$265.33	$265.35	$265.30
7 purchase totals =	$972.94		$1,067.2964	$1,067.29	$1,067.30	$1,067.30