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	$117.31	5.400%	$123.6447	$123.64	$123.65	$123.60
Purchase #2	$201.76	6.127%	$214.1218	$214.12	$214.10	$214.10
Purchase #3	$38.44	12.809%	$43.3638	$43.36	$43.35	$43.40
Purchase #4	$28.51	11.616%	$31.8217	$31.82	$31.80	$31.80
Purchase #5	$61.60	7.872%	$66.4492	$66.45	$66.45	$66.40
Purchase #6	$83.49	11.368%	$92.9811	$92.98	$93.00	$93.00
Purchase #7	$90.54	11.704%	$101.1368	$101.14	$101.15	$101.10
7 purchase totals =	$621.65		$673.5191	$673.51	$673.50	$673.40