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	$178.44	3.812%	$185.2421	$185.24	$185.25	$185.20
Purchase #2	$109.60	12.476%	$123.2737	$123.27	$123.25	$123.30
Purchase #3	$152.91	10.748%	$169.3448	$169.34	$169.35	$169.30
Purchase #4	$130.37	6.147%	$138.3838	$138.38	$138.40	$138.40
Purchase #5	$231.59	7.194%	$248.2506	$248.25	$248.25	$248.30
Purchase #6	$84.88	4.225%	$88.4662	$88.47	$88.45	$88.50
Purchase #7	$170.97	10.178%	$188.3713	$188.37	$188.35	$188.40
7 purchase totals =	$1,058.76		$1,141.3325	$1,141.32	$1,141.30	$1,141.40