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	$124.89	10.129%	$137.5401	$137.54	$137.55	$137.50
Purchase #2	$173.40	6.364%	$184.4352	$184.44	$184.45	$184.40
Purchase #3	$117.34	7.297%	$125.9023	$125.90	$125.90	$125.90
Purchase #4	$185.87	7.760%	$200.2935	$200.29	$200.30	$200.30
Purchase #5	$99.40	3.652%	$103.0301	$103.03	$103.05	$103.00
Purchase #6	$91.71	12.550%	$103.2196	$103.22	$103.20	$103.20
Purchase #7	$76.95	8.269%	$83.313	$83.31	$83.30	$83.30
7 purchase totals =	$869.56		$937.7338	$937.73	$937.75	$937.60