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	$230.25	11.133%	$255.8837	$255.88	$255.90	$255.90
Purchase #2	$35.83	8.498%	$38.8748	$38.87	$38.85	$38.90
Purchase #3	$83.69	12.460%	$94.1178	$94.12	$94.10	$94.10
Purchase #4	$188.50	3.561%	$195.2125	$195.21	$195.20	$195.20
Purchase #5	$46.41	12.753%	$52.3287	$52.33	$52.35	$52.30
Purchase #6	$213.93	11.343%	$238.1961	$238.20	$238.20	$238.20
Purchase #7	$38.69	4.190%	$40.3111	$40.31	$40.30	$40.30
7 purchase totals =	$837.30		$914.9247	$914.92	$914.90	$914.90