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	$178.40	12.181%	$200.1309	$200.13	$200.15	$200.10
Purchase #2	$78.35	13.760%	$89.131	$89.13	$89.15	$89.10
Purchase #3	$109.91	9.406%	$120.2481	$120.25	$120.25	$120.20
Purchase #4	$169.82	7.299%	$182.2152	$182.22	$182.20	$182.20
Purchase #5	$25.69	5.514%	$27.1065	$27.11	$27.10	$27.10
Purchase #6	$78.99	5.626%	$83.434	$83.43	$83.45	$83.40
Purchase #7	$78.80	11.214%	$87.6366	$87.64	$87.65	$87.60
7 purchase totals =	$719.96		$789.9023	$789.91	$789.95	$789.70