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	$79.63	3.244%	$82.2132	$82.21	$82.20	$82.20
Purchase #2	$44.57	13.119%	$50.4171	$50.42	$50.40	$50.40
Purchase #3	$110.45	13.346%	$125.1907	$125.19	$125.20	$125.20
Purchase #4	$181.37	8.458%	$196.7103	$196.71	$196.70	$196.70
Purchase #5	$80.74	10.434%	$89.1644	$89.16	$89.15	$89.20
Purchase #6	$77.79	11.377%	$86.6402	$86.64	$86.65	$86.60
Purchase #7	$90.44	12.827%	$102.0407	$102.04	$102.05	$102.00
7 purchase totals =	$664.99		$732.3766	$732.37	$732.35	$732.30