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	$113.44	9.614%	$124.3461	$124.35	$124.35	$124.30
Purchase #2	$127.78	6.682%	$136.3183	$136.32	$136.30	$136.30
Purchase #3	$133.49	13.263%	$151.1948	$151.19	$151.20	$151.20
Purchase #4	$48.30	9.559%	$52.917	$52.92	$52.90	$52.90
Purchase #5	$81.32	8.297%	$88.0671	$88.07	$88.05	$88.10
Purchase #6	$35.89	4.517%	$37.5112	$37.51	$37.50	$37.50
Purchase #7	$98.89	4.272%	$103.1146	$103.11	$103.10	$103.10
7 purchase totals =	$639.11		$693.4691	$693.47	$693.40	$693.40