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	$68.48	12.788%	$77.2372	$77.24	$77.25	$77.20
Purchase #2	$155.42	10.839%	$172.266	$172.27	$172.25	$172.30
Purchase #3	$6.41	9.339%	$7.0086	$7.01	$7.00	$7.00
Purchase #4	$206.26	8.749%	$224.3057	$224.31	$224.30	$224.30
Purchase #5	$235.27	9.797%	$258.3194	$258.32	$258.30	$258.30
Purchase #6	$214.27	11.223%	$238.3175	$238.32	$238.30	$238.30
Purchase #7	$28.80	11.681%	$32.1641	$32.16	$32.15	$32.20
7 purchase totals =	$914.91		$1,009.6185	$1,009.63	$1,009.55	$1,009.60