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	$53.41	12.734%	$60.2112	$60.21	$60.20	$60.20
Purchase #2	$76.88	8.171%	$83.1619	$83.16	$83.15	$83.20
Purchase #3	$149.94	10.260%	$165.3238	$165.32	$165.30	$165.30
Purchase #4	$80.46	4.788%	$84.3124	$84.31	$84.30	$84.30
Purchase #5	$31.32	5.868%	$33.1579	$33.16	$33.15	$33.20
Purchase #6	$89.85	7.216%	$96.3336	$96.33	$96.35	$96.30
Purchase #7	$53.30	3.822%	$55.3371	$55.34	$55.35	$55.30
7 purchase totals =	$535.16		$577.8379	$577.83	$577.80	$577.80