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	$73.77	6.196%	$78.3408	$78.34	$78.35	$78.30
Purchase #2	$78.88	13.264%	$89.3426	$89.34	$89.35	$89.30
Purchase #3	$138.59	12.302%	$155.6393	$155.64	$155.65	$155.60
Purchase #4	$166.64	7.378%	$178.9347	$178.93	$178.95	$178.90
Purchase #5	$36.41	7.461%	$39.1266	$39.13	$39.15	$39.10
Purchase #6	$5.84	11.578%	$6.5162	$6.52	$6.50	$6.50
Purchase #7	$162.48	10.376%	$179.3389	$179.34	$179.35	$179.30
7 purchase totals =	$662.61		$727.2391	$727.24	$727.30	$727.00