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	$93.66	9.355%	$102.4219	$102.42	$102.40	$102.40
Purchase #2	$249.78	3.106%	$257.5382	$257.54	$257.55	$257.50
Purchase #3	$101.93	9.385%	$111.4961	$111.50	$111.50	$111.50
Purchase #4	$39.94	3.110%	$41.1821	$41.18	$41.20	$41.20
Purchase #5	$62.63	13.851%	$71.3049	$71.30	$71.30	$71.30
Purchase #6	$146.40	6.242%	$155.5383	$155.54	$155.55	$155.50
Purchase #7	$112.90	6.564%	$120.3108	$120.31	$120.30	$120.30
7 purchase totals =	$807.24		$859.7923	$859.79	$859.80	$859.70